Photosynthesis of cotton near-isogenic lines introgressed with QTLs for productivity and drought related traits

Quantitative trait loci (QTLs) for yield and drought related traits were exchanged via marker-assisted selection (MAS) between elite cultivars of two cotton species, Gossypium barbadense (GB) cv. F-177 and Gossypium hirsutum (GH) cv. Siv’on. The resulting near-isogenic lines (NILs) manifested in many cases the expected drought-adaptive traits, but rarely exhibited an advantage in yield relative to the recipient parents. In the current study we characterized the photosynthetic activity of two selected NILs and their recipient parents under dryland and irrigated field conditions. The GB NIL exhibited a stable net rate of CO2 assimilation (A) across a wide range of leaf water potentials with a notable advantage over its recipient parent, F-177, under severe drought, associated with lower stomatal limitation, greater maximum velocity for carboxylation of Rubisco and greater electron transport rate. The GH NIL exhibited greater mesophyll conductance under drought conditions than its recipient parent, Siv’on, but these genotypes did not differ in A. Nevertheless, both NILs did not differ from their recipient parents in yield. This study provides further support to our previous conclusion that MAS is a useful means to enhance drought-adaptive traits of cotton but complimentary conventional breeding is required to achieve high yield potential.