Chlorophyll Fluorescence-Derived Photosynthetic Parameters and Yield of Common Bean (Phaseolus vulgaris L.) Under Multiple Stress and Drought.

Drought and intermittent drought stress are increasing and therefore affecting common bean production. Such changes in climate therefore require new approaches to plant improvement. Hence, a new device called a MultispeQ was used in this study to collect various parameters for phenotyping common bean (Phaseolus vulgaris L.) under different conditions. The objectives of the study were to assess plant response to PQ_SPAD (chlorophyll content), PhiII, PhiNPQ, and PhiNO (photosynthetic parameters) multiple stress, drought stress and non-stress; and to evaluate 13 genotypes (2 Andean lines, 10 Middle American lines and 1 non-nodulating check) for drought tolerance, Carbon isotope discrimination (CID), Nitrogen derived from the atmosphere (Ndfa), grain yield and yield components. The results found that under intermittent and terminal drought, PhiII and PhiNPQ decreased while PhiNO increased because of the reduction in photosynthetic efficiency coupled with the loss of non-photochemical quenching and the increased non-regulated losses, respectively. There were positive significant correlations between plant and seed Ndfa; and also between plant and seed CID. Genotypes responded differently especially for seed CID and Ndfa under the different conditions. It was also noted that some of the genotypes with high pod harvest index (PHI) also had high yields under drought. Interestingly, the identified drought tolerant Middle American genotypes (PT11_13, PT9_5_6, Longspeak, and Monterrey) with an increased PQ_SPAD at 75 days after planting (DAP), also had higher yield, and PHI. Thus, the identified genotypes may serve in breeding programs as parents for drought tolerance.