Adaptive responses of wild mungbean (Vigna radiata ssp. sublobata) to photo-thermal environment. II. Growth, biomass, and seed yield

Abstract

The leaf growth, dry matter production, and seed yield of 11 wild mungbean (Vigna radiata ssp. sublobata) accessions of diverse geographic origin were observed under natural and artificial photoperiod–temperature conditions, to determine the extent to which genotypic differences could be attributed to adaptive responses to photo-thermal environment. Environments included serial sowings in the field in SE Queensland, complemented by artificial photoperiod extension and controlled-environment growth rooms. Photo-thermal environment influenced leaf growth, total dry matter production (TDM), and seed yield directly, through effects of (mainly cool) temperature on growth, and indirectly, through effects on phenology. In terms of direct effects, leaf production, leaf expansion, and leaf area were all sensitive to temperature, with implied base temperatures higher than usually observed in cultivated mungbean (V. radiata ssp. radiata). Genotypic sensitivity to temperature varied systematically with accession provenance and appeared to be of adaptive significance. In terms of the indirect effects of photo-thermal environment, genotypic and environmental effects on TDM were positively related to changes in total growth duration, and harvest index was negatively related to the period from sowing to flowering, similar to cultivated mungbean. However, seed yield was positively related to the duration of reproductive growth, reflecting the indeterminate growth habit of the wild accessions. As a consequence, the wild accessions are more responsive to favourable environments than typically observed in cultivated mungbean, which is determinate in habit. It is suggested that the introduction of the indeterminate trait into mungbean from the wild subspecies would increase the responsiveness of mungbean to favourable environments, analogous to that of black gram (V. mungo). Although the wild subspecies appeared more sensitive to cool temperature than cultivated mungbean, it may provide a source of tolerance to the warmer temperatures experienced during the wet season in the tropics.