Varietal differences in photosynthesis, growth and yield responses of beans (phaseolus vulgaris L.) under different watering levels

Abstract

A study was conducted during the dry periods of 1990 in the field and in the greenhouse at the University of Nairobi's Faculty of Agriculture Farm, Kabete to investigate varietal differences in photosynthesis, growth and yield responses of beans (Phaseolus vulgaris L.) under different watering regimes. Four indigenous bean varieties ('Ulonzo', "Pinto', 'Zebra beans', 'White Haricot') from marginal rainfall areas, four ('Rosecoco (Merul', 'Pocho', 'Local', Okuodo) from high rainfall areas were used along with the two improved varieties ('GLP-1004' and 'GLP-2') which have been developed for marginal and high rainfall areas respectively. Watering treatments were imposed from seed emergence to late podding stages ' using a line-source sprinkler irrigation system in Experiment I and differential irrigation frequency in Experiment II. Photosynthesis and leaf area (LA)were measured using infra-red gas analyser and a Li-COR automatic LAintegrator respectively. Results showed that Ulonzo consistently had higher net photosynthetic rates than the other varieties under both watering levels. It was also observed that varieties from marginal rainfall areas, in general had higher photosynthetic values than those from high rainfall areas. Ulonzo also out yielded all the other varieties and as with photosynthesis, it was also noticed that varieties collected from marginal areas generally gave higher yields than those from high rainfall areas. This study indicates that there are varietal differences in photosynthesis, growth and yield responses of beans and that varieties from marginal rainfall areas tend to perform better than those from high rainfall areas.