Leaf Gas Exchange and Growth Adjustments in Reticulates and Inodorus Melons Under Deficit Irrigation

In a two year (2011 and 2012) study three diverse melon (Cucumis melo L.) cultivars, Mission (cantaloupe; reticulatus type), Da Vinci (tuscan; reticulatus type) and Super Nectar (honeydew; inodorus type) were subjected to two irrigation rates (50% vs. 100% crop evapotranspiration, ET_c) to investigate their leaf gas exchange and growth responses under water deficit conditions in southwest Texas. In 2012, deficit irrigation (50% ET_c) significantly decreased above ground biomass (37%), leaf area (50%), leaf number (43%) and specific leaf area (14%), while leaf gas exchange, relative water content, water potential, chlorophyll fluorescence (Fv/Fm), and chlorophyll content (SPAD index) were not affected. However, in the drier year 2011, deficit irrigation significantly reduced the net photosynthetic rate (P_N) and stomatal conductance (g_s). Under 50% ET_c, P_N and g_s were maintained in cv. Da Vinci while decreased in Mission and Super Nectar. Deficit irrigation significantly reduced total fruit yield in Mission (26%), Da Vinci (31%) and Super Nectar (35%). Thus, the late maturing cv. Super Nectar appeared to be more sensitive to drought stress possibly due to a decrease in leaf area and P_N; while the early maturing cvs. Mission and Da Vinci escaped severe water deficit, and sustained leaf water status through improved root growth and leaf gas exchange adjustment, respectively. Further, total fruit yield had significant correlations with leaf area, leaf number and specific leaf area under 50% ET_c. These results suggest that leaf area and P_N can be used as potential traits for screening melon cultivars for water deficit conditions.