PG Diploma

An investigation was conducted at the Division of Seed Technology, Indian Agricultural Research Institute, New Delhi to study the effect of loss of viability on growth and yield of cowpea and to find out whether the deleterious effects due to loss of viability could be compensated by increasing the plant population per unit area. The treatments comprised of four levels of germinations (72, 63, 48 and 39 per cent) and two plant populations (20 and 40 plants/m2). The field experiment was laid out in a 4 x 2 factorial randomized block design with three replications. The crop was sown on 22nd of March, 1980 and harvested on 19th of July, 1980. The findings are summarized below:
1. In order to create variability in germination percentage accelerated ageing treatment was given. During accelerated ageing, seed deterioration was maximum between 2nd and 3rd week after treatment. There was no deterioration during the first week. The length of root, shoot and their dry weight did not vary much until 3rd week after treatment. However, there was a drastic reduction in these attributes during the 4th week.
2. The rate as well as total field emergence were inversely related to the seed deterioration.
3. Leaf area decreased with seed deterioration at the final phase of crop growth. Similarly the low population density was superior to the high one.
4. Regarding leaf dry weight, the control and the low population density were significantly superior to other treatments at the time of harvest.
5. Germination levels 72 and 63 per cent had significantly more stem dry weight per plant. Similarly the low population density registered higher dry matter accumulation in the stem.
6. The germination levels exerted no significant influence on plant height except at the final stage when control recorded the highest value. The effect of planting densities on height was also not markedly evident at any of the stages.
7. The low population density had invariably higher number of branches per plant at various stages of observation. Regarding the effect of germination levels, they were not statistically different.
8. Appearance of first flower was significantly earlier in the plants from deteriorated seed lots. The population density had no marked bearing on this aspect.
9. Total dry matter yield was highest in the plants from the maximum deteriorated seed lot during the early stage. However, at later stages the control plants accumulated maximum dry matter which was on par with the 63 per cent germination level.
10. Relative growth rate was least in the maximum deteriorated seeds in the beginning. But control registered the least value during the period between 45 and 103 days after sowing. The 63 per cent and 48 per cent germination levels were having significantly higher values at this stage.
11. The various yield components were not significantly influenced by the germination levels. However, population density had a marked bearing on the pod dry weight per plant and the dry weight of pod covers.
12. The low population density tended to increase the leaf nitrogen content at the final stage. However, the interaction effects were significant on the 45th day after sowing, with maximum leaf nitrogen content in the low population- 63 per cent germination combination.
13. With regard to stem nitrogen content, the control and 63 per cent germination level were significantly superior to other deteriorated lots at the final phase of crop growth. Similarly the plants of high density planting had remarkably more stem nitrogen than the low density.
14. Neither the germination level nor the population density did significantly influence grain nitrogen content.
15. Nitrogen uptake followed the same trend as that of total dry matter yield except in the case of total nitrogen uptake per hectare with reference to the population density.
From this study, therefore, we may conclude that the four germination levels can be grouped into two distinct categories considering the loss of viability- yield relationships in cowpea. The control and the 63 per cent constitutes the first group, where no deleterious effects of seed deterioration was noted. The 48 and 39 per cent germination levels forms the second group where a significant reduction in terms of various growth attributes and dry matter yield was observed. This would, then, mean that the use of old seeds would not have a significant effect on yield, provided that viability is around 60 per cent and appropriate compensatory seed rates are used to allow for that fraction of seed population which is non- viable.