Genetic variation for stress-related traits in guar

Abstract

Eighty-two guar, Cyamopsis tetragonoloba (L.) Taub., germplasms were evaluated in laboratory and field studies for traits assumed to be associated with drought resistance. Primary root and lateral root lengths were measured in 10-day-old seedlings grown in polyethylene growth pouches at 35°C. Germplasms differed significantly in primary root and lateral root lengths, number of laterals, and in branching intensity (Experiment 1). Four vascular bundles were found in each germplasm with exception of a wild species, C. serrata Schinz, which had only three in each root. Germplasms differed significantly in canopy temperature and paraquat reaction (Experiment 2). Mean canopy temperatures exceeded air temperature ( T c − T a ), varying from 0.3 to 3.9°C in the 82 germplasms. Paraquat reaction (a relative measure of the plant's cellular antioxidant system) indicated five germplasms possessed a three-fold greater resistance to paraquat than the most susceptible germplasms. The uptake of paraquat was not significantly different in pubescent (non-waxy) and glabrous (waxy) germplasms. A stress index, designed to identify germplasms with vigorous root systems, high canopy temperature avoidance and resistance to paraquat, indicated 10 germplasms possessed relatively high levels of all traits. Seedling root characteristics, canopy temperature and paraquat reaction were not significantly correlated with grams seed −1 plant −1, suggesting that selection for improved yield using root and plant measurements described above would be non-productive.