Physiological basis of yield differences in bean (phaseolus vulgaris L.) cultivars

Abstract

The study was conducted at the University of Nairobi Facul ty of Agr icul ture Farm, Kabete, located on la ti tude 10 5 I south and longitude 36° 44 I east at an altir.ude of about 1800 metres above sea level. The study investigated the following physiological crop parameters: leaf net photosynthetic rates, leaf nitrogen, specific leaf weight, leaf area indices and stem non-structural carbohydrate contents. Plant biomass accumulation was also determined. These parameters were taken at fortnight ly intervals from (f lower ing phase of growth) 32 days after t i 11 ma t u r i t Y emergence in ten (DAE) bean (phaseulus vulgaris L.) cultivars namely: Pocho, GLP-92, White Har i cot., GLP-1004, GLP-2, GLP-24, Ulonzo, E-l, E--3 and E-5. The study was done in .two different seasons; with the first season experiment (experiment 1) running from 29th March, 1994 to 8th of July 1994. Second season experiment (exper imen t I I) was conducted from 12th of October 1994 to 10th of January, 1995. The results of the study revealed a variation of the above mentioned physiological parameters among cul ti vars. Leaf net photosynthetic rate and leaf nitrogen contents had a positi ve correlation at 45 DAE (pod set). There was also positive correlation between photosynthetic rates and yields. These parameters differences were however not the best indices for yield among cultivars since even higher yielding cultivars such as Pocho, E-l, E-3, and E-5 had relatively lower performance in these characters. Non-structural carbohydrate remobilization from the stem contents at pod set about 45 DAE) seemed to be a good indicator for yield differences among bean cultivars. Specific leaf weight variation was more stable as a result of environmental changes and therefore was proposed a good index for the basis of yield differences among cultivars. Harvest index (HI), apparent harvest index (AHI) in this case, was also promising indicator of yield differences