ABSTRACT
This experiment was conducted at the Federal University of Agriculture Teaching and Research Farm Makurdi, Benue state during the 2016 cropping season to study the effect of ageing on germination and yield of two cowpea varieties stored for a year, two years and three years. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. Data were collected on emergence percentage, seed conductivity seed value, pod length, pod weight, number of seeds/pod, seed weight, 100 seed weight, and pod per plant. Results showed that significant difference occurred among the varieties for all the traits measured except for germination percentage, pod length per plant, number of seed per plant, pod weight per plant and pod per plant. Also, seed conductivity value and pod length per plant were significant across years while the rest traits weren’t significant. For variety x year interaction effect, all the parameters were significant except emergence percentage and 100 seed weight. Germination percentage of the two varieties evaluated were not affected by ageing. Seeds of ITO7K-3O3-1 stored for one and two years showed high seed conductivity value implicating impairment of seed membrane while ITO7K-298-15 seeds stored for 3 years had the least conductivity value indicating higher seed quality. This also indicates that seeds stored for longer periods were able to repair themselves during storage. Seeds of ITO7K-3O3-1 stored for 2 years gave the highest yield of 2054kg/ha while ITO7K-298-15 seeds stored for 2 years had the least yield of 787.33kg/ha. Cowpea seeds can be stored for up to three years and still be used as planting materials provided the required storage conditions are maintained.
CHAPTER ONE
1.0 Introduction
Cowpea [Vigna unguiculata (L) Walp] is an important crop in the dry savannah of West and Central Africa (Kamara et al., 2008). It is a major source of dietary protein in many parts of the world, particularly in countries situated along the tropical and subtropical belt, where availability and consumption of animal proteins is low because of social and economic constraints (Mortimore et al., 1997).
An estimated 14.5 million hectares planted to cowpea annually with a conservative estimate of 5.7 million metric tons of dried grain (FAO 2013). Cowpea is cultivated over a wide range of agro-environments in Nigeria ranging from the forest in the South to the Sahel savannah in the North, although the bulk of production is in the northern drier part of the country (Akande and Balogun 2009).
Among the legumes, cowpea is the most extensively grown, distributed, and traded food crop consumed (Agbogidi, 2010) and almost every part of the cowpea plant is useful to humanity. The green pods, leafy greens, fresh shelled green peas, and shelled dried peas of cowpea are used for human consumption and animal feeds (Singh et al., 2003). It does well and is more popular in semi-arid tropics where other food legumes do not perform well (Sankie et al., 2012).
In addition, cowpea is shade tolerant and therefore, compatible as an inter-crop with maize, millet, sorghum, sugar cane, and cotton.
This makes cowpea an important component of traditional inter cropping systems (Singh, 2002; 2005).
Its cultivation is not without challenges as the productivity is low due to attacks from insect pests and disease, inefficient cropping systems and low yield potential of local varieties (Ajeigbe and Singh, 2006). To ensure food security, there is need for further research on cowpea to overcome the challenges limiting its cultivation and production.
Quality seed is the prime factor for crop productivity but seed ageing is one of the main causes of reduction in seed quality (FAO/IPGRI 1994). This could as a result of poor quality seeds used by farmers as a result of ageing. Since our farmers use farm saved seed, it is important to investigate on seed storage and mechanism of ageing of cowpea seeds. The present work was therefore undertaken to investigate the effects of ageing on the physiology of cowpea seeds.
1.1 Objectives of study
- To determine the effect of seed ageing on the viability and vigour of cowpea seeds.
2) To investigate the influence of seed ageing on yield of cowpea.
CHAPTER TWO
2.0 Literature review
2.1 Origin and distribution of cultivated cowpea
Cowpea [Vigna unguiculata (L) Walp] is a member of phaseoleae tribe of the sub-family Papilanioidae of the Fabaceae family (Singh et al., 2005). It is believed that the name cowpea probably originated from the use of the plant as an important source of hay for cows in the South-eastern United States and in other parts of the world. (Food security, 2010).
Where cultivated cowpea originated from has been a matter of speculation and discussion for several years. The controversial centre of domestication event of cowpea is now recognized as occurring in the northern part of Africa (Coulibaly et al., 2002).
West and Central Africa was suggested to be the secondary centre of diversity. Studies by (Padulosi et al., 1991), and (Padulosi 1993), strongly indicated that the highest genetic diversity of primitive wild forms of cowpea can be found in the region of the African continent currently encompassed by Namibia, Botwana, Zambia, Zimbabwe, Mozambique, Swaziland, and South Africa, with the most primitive species observed in Transvaal, Cape town and Swaziland.
Based on this later observation, Padulosi and Ng (1997) suggested that Southern Africa may be the site of origin of cowpea with subsequent radiations of the primitive forms to other parts of Southern and eastern Africa, and subsequently to West Africa and Asia Ng (1995) and Ba et al., (2004) suggested that the small seed size of wild cowpeas likely facilitated their dispersed by birds throughout East and West Africa contributing to the diversity and development of secondary wild forms.
Human selection for larger seeds and better growth habits from natural variants in wild cowpeas likely led to diverse culti-groups and their domestication in Asia and in Africa.
Cowpea can be grown under rain fed conditions as well as by using irrigation or residual moisture along river or lake flood plains during the dry season, provided that the range of temperature is between 28 and 30℃
(night and day) during the growing season. Cowpea performs well in agro ecological zones where the rainfall range is between 500 and 1200mm/year. However, with the development of extra early and early maturing varieties, the cowpea crop can thrive in the Sahel where the rainfall is less than 500mm/year. This is because cowpea is tolerant to drought and well adapted to sandy and poor soils.
2.2.0 Seed Quality
Cowpea seed quality is seen in terms of physical, physiological and genetic qualities (Olasoji et al., 2013). Seed is a basic input in agriculture. Strictly speaking seed is an embryo, a living organism embedded in the supporting or the food storage tissue. In seed, the importance is given to the biological existence whereas; in grain the importance is given to the supporting tissue the economic produce.
2.2.1 Components of seed quality
Seed quality is the possession of seed with required genetic and physical purity that is accompanied with physiological soundness and health status. The major seed quality characters are summarized as below.
- Physical Quality: It is the cleanliness of seed from other seeds, debris, inert matter, diseased seed and insect damaged seed. The seed with high quality should have uniform size, weight, and colour and should be free from stones, debris, and dust, leafs, twigs, stems, flowers, fruit as well as without other crop seeds and inert material. It also should be devoid of shrivelled, diseased mottled, moulded, discoloured, damaged and empty seeds. The seed should be easily identifiable as a species of specific category of specific species. Lack of this quality character will indirectly influence the field establishment and planting value of seed. This quality character could be obtained with seed lots by proper cleaning and grading of seed (processing) after collection and before sowing / storage.
- Genetic purity: It is the true to type nature of the seed. i.e., the seedling plant tree from the seed should resemble its mother in all aspects. This quality character is important for achieving the desired goal of raising the crop either yield or for resistance or for desired quality factors.
- Physiological Quality: It is the actual expression of seed in further generation / multiplication. Physiological quality characters of seed comprises of seed germination and seed vigour. A viable seed is one which is capable of germination under suitable conditions (Bradbeer 1988) while seed vigour is defined as the sum total of those properties of the seed which determines the level of activity and performance of the seed of seed lot during germination and seedling emergence (ISTA). The difference in seed vigour is the differential manifestation of the deteriorative process occurring in the seed before the ultimate loss of ability to germinate. Physiological quality of seed could be achieved through proper selection of seed (matured seed) used for sowing and by caring for quality characters during extraction, drying and storage.
- Seed Health - Health status of seed is nothing but the absence of insect infestation and fungal infection, in or on the seed. Seed should not be infected with fungi or infested with insect pests as these will reduce the physiological quality of the seed and also the physical quality of the seed in long term storage. The health status of seed also includes the deterioration status of seed which is expressed through low vigour status of seed. The health status of seed influences the seed quality characters directly and warrants soundness of seed for the production of elite seedlings at nursery / field.
2.3 SEED STORAGE
Seed storage is defined as the preservation of seed with initial quality until it is needed for planting.
2.3.1 Stages of Seed Storage
Seed storage starts from the field after physiological maturity, so seeds could be stored on plant or in storage facilities. After harvesting the seeds are either stored in ware houses or in transit or in retail shops. During the old age days, the farmers were used farm saved seeds, in little quantity, but introduction of high yielding varieties and hybrids and modernization of agriculture necessitated the development of storage techniques to preserve the seeds. The practice of storing the
seeds starts from the ancient days itself, following simple and cheap techniques e.g. placing the seeds in salt, red earth treatment to red gram etc
2.3.2 Purpose of seed storage
Seed storage is the maintenance of high seed germination and vigour form harvest until planting. Is important to get adequate plant stands in addition to healthy and vigorous plants. Every seed operation has or should have a purpose. The purpose of seed storage is to maintain the seed in good physical and physiological condition from the time they are harvested until the time they are planted. Seeds have to be stored, of course, because there is usually a period of time between harvest and planting. During this period, the seed have to be kept somewhere. While the time interval between harvest and planting is the basic reason for storing seed, there are other considerations, especially in the case of extended storage of seed.
Seed suppliers are not always able to market all the seed they produce during the following planting season. In many cases, the unsold seed are “carried over” in storage for marketing during the second planting season after harvest. Problems arise in connection with carryover storage of seed because some kinds, varieties, and lots of seed do not carryover very well. Seeds are also deliberately stored for extended periods so as to eliminate the need to produce the seed every season. Foundation seed units and others have found this to be an economical, efficient procedure for seed of varieties for which there is limited demand. Some kinds of seed are stored for extended periods to improve the percentage and rapidity of germination by providing enough time for a “natural” release from dormancy.
Regardless of the specific reasons for storage of seed, the purpose remains the same maintenance of a satisfactory capacity for germination and emergence. The facilities and procedures used in storage, therefore, have to be directed towards the accomplishment of this purpose.
In the broadest sense the storage period for seed begins with attainment of physiological maturity and ends with resumption of active growth of the embryonic axis, i.e., germination. Seeds are considered to be physiologically and morphologically mature when they reach maximum dry weight. At this stage dry-down or dehydration of the seed is well underway. Dry-down continues after physiological maturity until moisture content of the seed and fruit decreases to a level which permits effective and efficient harvest and threshing. This stage can be termed as harvest maturity. There usually is an interval of time between physiological maturity and harvestable maturity, and this interval represents the first segment of the storage period. Any delays in harvesting the seed after they reach harvest maturity prolongs the first segment of the storage period – often to the detriment of seed quality.
The second segment of the storage period extends from harvest to the beginning of conditioning. Seed in the combine, grain wagon, and bulk storage or drying bins are in storage and their quality is affected by the same factors that affect the quality of seed during the packaged seed segment of the storage period.
2.3.3 Storage condition and ageing of seeds
Common with all other living things, seeds are subjected to ageing and, eventually, to death .In the case of orthodox seeds, the process of ageing and deterioration is so greatly affected by the conditions of storage that the age of seeds, expressed solely in terms of the period elapsed since ripening and harvesting is an inadequate measure of the degree to which they have aged in the sense of losing viability and progressing towards the irreversible deterioration of death.
2.4 Effect of seed ageing on viability and vigour
Ageing is a common phenomenon in all the living entities, which results in progressive decline in all vital events ultimately leading to death. Seeds, which are the elements of propagation of a plant species for generations, also have specific and definite life spans which may vary in different genera, species and accessions or genotypes. Extensive research in the area of seed biology and seed technology during the last few decade has unravelled the mechanism of the degenerative processes which bring down the quality of seeds only to some extent due to immense variability among various kinds of seed. Extreme examples of ancient seed that had longevities of thousands of years such as the Arctic lupine seeds, which remained in the dormant viable state for more than ten thousand years, exist in the literature, such seeds fall in the category of desiccation tolerant or orthodox seeds. On the other hand, seeds of several genera belonging to the same category such as soybean, onion and groundnut do not have such extended longevities.
Many factors, both intrinsic and extrinsic, play important roles in keeping the quality of seeds. Several complex changes occur in seeds as seeds age in storage, and the rate of these changes depend on the conditions of storage. Regardless of the causal agents, changes in some quantifiable traits occur when seeds deteriorate, which can be used to estimate the rate of deterioration. An understanding of the mechanism of seed deterioration and the various physiological, biochemical and molecular changes associated with it is important to devise methods to control the rate of such deterioration in order to extend their longevity, and also develop reliable indices for measuring the ageing process. As seeds deteriorate and lose their germinability during periods of prolonged ageing (Ansari and Sharif Zadeh,
2013; Seidat et al., 2012). A study by Verma et al. (2003) indicated that seedling establishment and emergence rate are reduced with increase in seed storage duration. Ageing was manifested as reduction in germination percentage and those seeds that did germinate produced weak seedling (Veselova, Veselovsky, 2003). Also, (Basra et al., 2003) reported that percentage emergence decreased with accelerated ageing periods in cotton. They also reported that the decline in seed germination during accelerated ageing was accompanied with the increase in mean emergence time.
Electrical conductivity is related to the deterioration processes of seeds as degradation of cell membranes and leakage out of the cells (Delouche and Baskin 1973). The change of electric conductivity during seed soaking is commonly used as an indicator for testing the integrity of plasma membrane (Bewley and Black, 1994; Wang et al., 2003). Thus, many researchers have used electrical conductivity test to indicate seed vigour (Normash and Chin 1991). Seed vigour measures the sum total of those properties of the seed which determine the level of activity and performance of the seed or the seed lot during germination and emergence. The vigour of seeds stored even at low temperatures decline over time due to ageing. Rina et al., 2008 reported that electrical conductivity of seed leachate increased with increasing seed age in soybean.
2.5 Effect of seed ageing on cowpea yield
Pod length is one of the yield attribute controlled by genes. (Johnson et al., 2011) reported that ageing did not affect cowpea seeds at harvest. He also reported that differences in the 100 seed weight of aged seeds can be attributed to varietal differences as there was no significant difference in the 100 seed weight of old and new cowpea seeds.
In a research by (Johnson et al., 2011) there was no significant difference in the number of seed per pod between evaluated old and new seed. (Rina et al., 2008) reported an increasing number of pod per plant in soybean plant with an increasing ageing period. (Grieve et al., 1992) reported that ageing affects leaf appearance rate and this might lead to reduced yield potential by lengthening the days from sowing to complete ground cover and a delay in the establishment of an optimum canopy (Soltani et al., 2001). Optimum canopy establishment is required to minimize inter plant competition and to maximise crop yield. High vigor seed lots show rapid and uniform seedling emergence, leading to the production of vigorous plants and optimum stand establishment (Dalil et al., 2010), which may increase grain yield (Ghassemi-Golezani et al., 2010). Several reports have shown that seed deterioration causes poor stand establishment in the field and consequently yield loss of canola (Ghassemi-Golezani et al., 2010) and lentil (Chadordooz-Jeddi et al., 2013). Seed deterioration may result in lower tolerance to environmental stresses (Khan et al., 2003). Yield of old cowpea seeds was not significantly different from new seeds of the same variety (Johnson et al., 2011). A significant total seed weight is an indication that variability exists in the yield potentials of the cowpea varieties used.
CHAPTER THREE
MATERIALS AND METHODS
3.0 LOCATION AND PERIOD OF EXPERIMENT
The experiment was conducted at the Federal University of Agriculture teaching and research farm Makurdi, Benue state between latitude 7.76°N and longitude 8.62°E at an elevation of about 103m above sea level during the 2016 cropping season.
3.1 PLANTING MATERIALS
Two varieties of cowpea were used. The seed lots are ITO7K-298-15 and ITO7K-303-1. The following seed lots were obtained from these varieties based on the age of seeds. These seeds were stored in the seed room of the Molecular Biology Laboratory of the Federal University of Agriculture, Makurdi.
3.2.0 SEED QUALITY TEST
These seed lots were subjected to seed quality tests namely: conductivity test in the laboratory and field evaluation for emergence % and yield.
3.2.1 CONDUCTIVITY TEST
Three replicates of 50 pre weighed seeds from each variety were soaked for about 24 hours in 100 ml distilled water in 200-250ml beakers and covered with aluminium foil to prevent contamination. A beaker of distilled water without seeds was prepared as control. Seed conductivity value was measured using a Hanna instrument (H198129) conductivity meter. The results were expressed on a dry-weight basis in µs cm-1g-1 as;
Conductivity per gram of seed= conductivityµS for each flask-conductivity of distilled waterdry weightgof seed sample
(Zhao et al., 2007)
3.2.2 EMERGENCE PERCENTAGE
Emergence data was collected and emergence percentage was calculated using:
Emergence percentage=100×number of seedlings emergedtotal number of seeds planted
(Roberval et al., 2004)
3.3.0 AGRONOMIC PRACTICES
3.3.1 LAND PREPARATION
Land clearing was done with the use of cutlass while ridges were manually done with hoe.
3.3.2 EXPERIMENTAL DESIGN AND LAYOUT
The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications.
3.3.3 PLANTING
Sowing was done on the 31st of august 2016. Two seeds were planted per hill at an intra-row spacing of 20cm×60cm with total plant population of 52941/ha
3.3.4 WEEDING
Hand weeding was done some days after planting while hoe weeding was done at 4 weeks after planting (WAP).
3.3.5 FERTILIZER APPLICATION
SSP fertilizer was applied using band placement at a rate of 64.34kg/ha, 4 weeks after planting.
3.3.6 HARVESTING
At agronomic maturity, the cowpea pods were harvested from the field.
3.4 DATA COLLECTION ON THE FIELD
At agronomic maturity, some agro-morphological and physiological data were collected. Five (5) plants were sampled per plot for data collection on following parameters;
- Pod length (cm) - Five pods were sampled from each plot and their lengths were measured using a rule. The pod length was determined by measuring the length of the pod from the base of the peduncle to the tip of the pod
- Pod weight- After harvest, the total pods from the five sampled plants were collected and weighed using a sensitive scale. The mean was obtained by dividing the total weight by five.
- Number of seeds/pod-Five cowpea pods were randomly sampled from each plot and the total number of seeds obtained from the pods was divided by five to obtain the mean number of seeds per pod for each plot.
- Yield – At harvest, the plant used above were harvested separately. The yield for each plot was determined by weighing each sample and dividing by five to obtain the yield per plant for each plot.
- 100 seed weight (g) –Hundred seeds were counted from each plot and weighed with a sensitive scale.
- Pod per plant-The number of pods from five plants was counted and divided by five to obtain the mean number of pods per plant for each plot.
3.5 STATISTICAL ANALYSIS
Data collected were subjected to Analysis of Variance (ANOVA) using Minitab 17 and treatments means were separated using (FLSD) at 5% level of probability.
CHAPTER 4
4.0 Results
Table 1 is the table of means showing the effect of seed ageing on two cowpea variety with respect to some physiological and agronomic parameters. Across the varieties used, there was no difference in emergence percentage, pod length per plant, number of seed per plant, pod weight per plant and pod per plant but differences were observed in the conductivity value, 100 seed weight and seed weight per kilogram per hectare. ITO7K-298-15 seeds had the least seed conductivity and 100 seed weight value of 24.46 and 19.06 respectively. ITO7K-303-1 however, had the highest seed weight per kilogram per hectare value of 1608.67.
Table 2 is the table of means showing the effect of seed ageing on year for the different physiological and agronomic parameters. Statistical differences were observed in pod length per plant and conductivity while emergence percentage, 100 seed weight, number of seed per plant, pod weight per plant, pod per plant and seed weight per kilogram per hectare were statistically the same. There was an ascending trend in vigour with increase in year of storage. Cowpea seeds stored for three years had the highest vigour value while those stored for a highest had the least vigour value. The highest pod length was observed in cowpea seeds stored for two years while those stored for a period of one and three years gave the least pod length per plant value.
|
Variety
|
E%
|
Cond(µs)
|
Pl/plt(cm)
|
100Sw(g)
|
Ns/plt
|
Pw/plt(g)
|
Pod/plt
|
Yield/kg/ha
|
|
ITO7K-298-15
|
81.39a
|
24.46b
|
15.48a
|
19.06b
|
77.80a
|
23.21a
|
10.36a
|
1072.44b
|
|
ITO7K-303-1
|
72.51a
|
50.86a
|
15.80a
|
24.17a
|
94.53a
|
23.21a
|
12.22a
|
1608.67a
|
|
Mean
|
76.95
|
37.66
|
15.64
|
21.62
|
86.17
|
23.21
|
11.29
|
1340.56
|
|
SE
|
3.71
|
1.28
|
0.33
|
0.74
|
5.21
|
1.12
|
0.56
|
72.10
|
Table 1: The response of cowpea varieties to ageing on physiological and agronomic traits in Makurdi during 2016 cropping season
Means that do not share a letter are significantly different.
E%=Emergence percentage Cond= Conductivity 100SW= 100 seed weight NS/plt=Number of seed per plant
PW/plt=Pod weight per plant Pl/plt=Pod length per plant Plt=plant SE=standard error
Table 2: Table of means showing the effects of age on the physiological trait of cowpea variety in Makurdi during the 2016 cropping season.
|
Year
|
E%
|
Cond(µs)
|
Pl/plt(cm)
|
100sw(g)
|
Ns/plt
|
Pw/plt(g)
|
Pod/plt
|
Yield/kg/ha
|
|
2013
|
83.34a
|
17.16c
|
14.64b
|
23.57a
|
89.53a
|
23.20a
|
11.67a
|
1411.00a
|
|
2014
|
75.21a
|
38.08b
|
17.19a
|
21.80ab
|
83.43a
|
20.78a
|
11.30a
|
1420.67a
|
|
2015
|
72.29a
|
54.73a
|
15.09b
|
19.47b
|
85.53a
|
18.47a
|
10.90a
|
1190.00a
|
|
|
Mean
|
76.95
|
36.66
|
15.64
|
21.61
|
86.16
|
20.82
|
11.29
|
1340.56
|
|
SE
|
5.24
|
1.81
|
0.46
|
1.05
|
7.37
|
1.58
|
0.80
|
102.00
|
| |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Means that do not share a letter are significantly different.
E%=Emergence percentage Cond= Conductivity 100SW= 100 seed weight NS/plt=Number of seed per plant
PW/plt=Pod weight per plant Pl/plt=Pod length per plant Plt=plant SE=standard error
Table 3 is the mean table for variety x year interaction as affected by seed ageing. A non-significant effect was recorded in emergence percentage and 100 seed weight while pod length per plant, number of seed per plant, pod weight per plant, pod weight per plant and pod per plant had significant value. A high significant effect was however observed in conductivity and seed weight per kilogram per hectare. An increase in vigour as a result of an increase in the length of storage was a trend observed from the two varieties evaluated. ITO7K-303-1 seeds stored for three years had the highest conductivity value of 26.20 while the least was from ITO7K-298-15 seeds stored for one and two years. ITO7K-303-1 seeds stored for two years had the highest number of seed per plant of 109.87 while the least was from ITO7K-298-15 seeds stored for two years. The highest pod weight per plant was recorded in ITO7K-303-1 seeds stored for two and three years while the lowest was from ITO7K-303-1 and ITO7K-298-15 seeds stored for three and two years respectively. ITO7K-303-1 seeds stored for two years had the highest pod per plant while ITO7K-298-15 seeds stored for two years gave the lowest pod per plant. In seed weight per kilogram per hectare, ITO7K-303-1 seeds stored for two years gave the highest yield while the lowest was recorded from ITO7K-303-1 seeds stored for a year and those of ITO7K-298-15 stored for three and two years.
Table 3: The variety x year interaction effect on physiological and agronomic traits of two cowpea varieties in Makurdi during 2016 cropping season
|
Variety
|
Year
|
E%
|
Cond(µs)
|
Pl/plt(cm)
|
100Sw(g)
|
Ns/plt
|
Pw/plt(g)
|
Pod/plt
|
Yield/kg/ha
|
|
ITO7K-298-15
|
2013
|
85.83a
|
10.37d
|
10.34a
|
20.93abc
|
74.80abc
|
21.43ab
|
10.40abc
|
1129.33c
|
|
ITO7K-298-15
|
2014
|
80.83a
|
15.79cd
|
11.12a
|
17.67c
|
57.00c
|
12.89b
|
8.40c
|
787.33c
|
|
ITO7K-298-15
|
2015
|
77.50a
|
41.22b
|
10.47a
|
18.57c
|
101.6ab
|
20.96ab
|
12.27abc
|
1300.67bc
|
|
ITO7K-303-1
|
2013
|
80.85a
|
23.96c
|
10.21a
|
26.20a
|
104.27ab
|
24.97a
|
12.93ab
|
1692.67ab
|
|
ITO7K-303-1
|
2014
|
69.58a
|
60.37a
|
10.60a
|
25.93ab
|
109.87a
|
28.67a
|
14.20a
|
2054.00a
|
|
ITO7K-303-1
|
2015
|
67.08a
|
68.24a
|
11.00a
|
20.37bc
|
69.47bc
|
15.99b
|
9.53bc
|
1079.33c
|
|
Mean
|
|
76.95
|
36.66
|
10.62
|
21.61
|
86.17
|
20.82
|
11.29
|
1340.56
|
|
SE
|
|
5.24
|
1.81
|
0.46
|
1.05
|
7.37
|
1.58
|
0.80
|
102.00
|
Means that do not share a letter are significantly different.
E%=Emergence percentage Cond= Conductivity 100SW= 100 seed weight NS/plt=Number of seed per plant
PW/plt=Pod weight per plant Pl/plt=Pod length per plant Plt=plant SE=standard error
CHAPTER FIVE
5.0 Discussion
5.1 Effect of ageing on viability and vigour
Viability of the cowpea varieties was not affected seed ageing for the three years period in this study. It was observed that older seeds had higher seed quality than the newer ones under air conditioned storage environment. It could be that these seeds had self – repair at the initial stage of storage which was maintained due to appropriate storage condition. Mohammedi et al. (2011) in soybean reported that seed ageing affects both seed germination and vigour. Soltani et al. (2008) in wheat reported that seed ageing reduces germination. Rina et al. (2008) in their study on soybean reported that electrical conductivity of seed leachate increased with increasing seed age. The findings of this study are at variance with the reports of (soltani et al., 2008) and (Rina et al., 2008). This study also disagrees with Mohammedi et al. (2011) on the effect of seed ageing on seed germination and vigour in soybean as ageing affects vigour in the study. The results however, corroborates the findings of Sung and Chiu (1995) in soybean, Parmoon et al. (2013) in pea and Khan et al. (2013) also in pea who attributed this increase in vigour to decreased activity of α- and β- amylase with time of storage, regardless the storage environment. The cool storage condition in this study could have kept these seeds in a glassy state and low seed water content leading to extremely high viscosity and low molecular mobility of the seed cytoplasm. The extremely high viscosity and low molecular mobility of the seed cytoplasm could prevent or inhibit many deleterious processes (Williams and Leopold, 1989; Sun and Leopold, 1993, 1994, 1998; Leopold et al., 1994; Leprince and Walters-Vertucci, 1995; Sun et al., 1998; Buitink et al., 1998, 2000)
5.2 Effect of ageing on some cowpea yield parameters
Yield in cowpea is dependent on variety. The crop overcomes the initial vigour differences expressed after seedling establishment in the field. Akhter et al. (1992) reported that after field establishment the effect of seed ageing is removed. This is supported by (Adetumbi et al., 2011) who reported that ageing did not affect the pod length of old and new cowpea seeds of the same variety. The varietal difference in 100 seed weight is genetically inclined as expressed in yield.
CHAPTER SIX
6.0 Conclusion and Recommendation
6.1 Conclusion
Ageing of cowpea seeds for 3 years did not influence its viability or yield. This work showed that these cowpea seeds have the ability for self- repair and improved its quality as the seeds aged especially when stored in a cooled environment. Also, conductivity test is a more sensitive test in dictating subtle physiological state of cowpea seeds than germination test.
6.2 Recommendation
I recommended storage of cowpea seeds for up to 3 years as there will be no adverse effect on its viability and vigour.
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APPENDIX
Analysis of variance for viability, vigour and yield of cowpea.
|
SOV
|
E%
|
PL/Plt(cm)
|
Cond(µs)
|
100 SW(g)
|
NS/Plt
|
PW/Plt(g)
|
Pod/Plt
|
Yield/kg/ha
|
|
Variety
|
355.11NS
|
0.44 NS
|
3629.24 **
|
117.56**
|
1260.02 NS
|
102.91 NS
|
15.68 NS
|
1293904**
|
|
Year
|
196.76 NS
|
11.16 *
|
2126.16**
|
25.38 NS
|
57.62 NS
|
33.52 NS
|
0.88 NS
|
102142 NS
|
|
Var x Year
|
17.37 NS
|
12.09*
|
362.19**
|
15.71 NS
|
2891.78*
|
163.37*
|
27.81*
|
831131**
|
|
Cv
|
11.29
|
15.64
|
36.66
|
21.61
|
86.17
|
20.82
|
11.29
|
1340.60
|
**: Significant difference at P≤ 0.001, *: Significant difference at P≤ 0.005, NS: not significant
SOV=Source of variation CV=coefficient of variation Var=variety E%=Emergence percentage Pl/plt=Pod length per plant
Cond= Conductivity 100SW= 100 seed weight NS/plt=Number of seed per plant PW/plt=Pod weight per plant
Plt=plant
Fig 1. Cowpea field during seedling stage
Fig 2. Cowpea field during flowering period