Rooting pattern and seed yield of selected pinto bean genotypes under different levels of soil moisture

Abstract

Dry bean (Phaseolus vulgaris) is currently being introduced for rainfed production in the Dark Brown soil zone in Saskatchewan. Insufficient water is one of the major factors limiting crop production in this soil zone. Ten pinto bean genotypes (Othello, Agate, GH196-2, 6315, 5325, Earliray, Fiesta, ISB82-354, UI 111 and Nodak) were exposed to drought stress in the field to study their rooting pattern under drought stress. Three pinto bean genotypes (Othello, Agate and GH196-2) with an extensive root system in the deeper soil layers and three (Earliray, Fiesta and ISB82-354) with a less extensive root system were exposed to drought stress and nonstress conditions in the growth room and in the field to study the relationship between rooting pattern and seed yield. In addition, three indeterminate pinto bean genotypes (Othello, Nodak and Fiesta) and three determinate genotypes (Agate, Agassiz and Earliray) were exposed to a soil moisture gradient to study the effects of soil moisture level on seed yield and other agronomic traits. Othello, Agate and GH196-2 had an extensive root system in the deeper soil layers, whereas Earliray, Fiesta and ISB82-354 had a less extensive root system in the deeper soil layers. An extensive root system in the deeper soil layers was associated with increased soil moisture depletion at those depths. Shoot dry mass, total root dry mass, mean root length density and root:shoot ratio were the same for the ten pinto bean genotypes. Pinto bean genotypes with an extensive root system (Othello, Agate and GH196-2) in the deeper soil layers had higher seed yield compared to genotypes with a less extensive root system (Earliray, Fiesta and ISB82-354) in the deeper soil layers in the field and in the growth room. Due to insufficient drought stress in the field, the rooting pattern of the six pinto bean genotypes was the same under irrigation and rainfed conditions. In the growth room, pinto bean genotypes with an extensive root system showed a stronger recuperative ability after a severe drought stress compared to genotypes with a less extensive root system. Root traits were positively correlated with seed yield under adequate soil moisture or where drought stress was relieved before maturity. Soil moisture deficit reduced number of pods per plant, plant height, seed weight, seed yield and seed nitrogen concentration of both determinate and indeterminate pinto bean genotypes. Indeterminate pinto bean genotypes had, on average, higher mean seed yield and showed a greater seed yield response to increasing soil moisture availability compared to determinate genotypes. However, the difference in seed yield of the two groups was small under high drought stress, except in the case of one very early maturing determinate genotype.