Comparison of fruit texture and aquaporin gene expression in papaya "Khak Nual" cultivated under varying conditions

The effects of cultivation conditions on the texture of unripe papaya fruit 'Khak Nual' were investigated. Fruit from papaya cultivated using raised bed conditions were crisper than those cultivated under open field conditions. Conversely, fruit cultivated under open field conditions were firmer. In all cases, mesocarp cells and intercellular spaces were larger in papaya fruit cultivated in raised beds, reflecting the higher relative humidity (RH) of the cultivation conditions and greater water availability. At harvest, TIP2-1, TIP4-1, SIP1 and PIP1-3 expression was significantly higher in fruit cultivated under raised bed conditions, which correlated with the larger cells of the mesocarp, the RH and the ready availability of water. There also appeared to be a link between aquaporin gene expression and crispness in papaya fruit from both conditions. Expression of TIP2-1 and TIP4-1 correlated with papaya fruit under open field conditions while SIP1 and PIP2-5 correlated with papaya fruit under raised bed conditions. The results clearly demonstrate the effect of cultivation conditions on fruit texture, with water availability being critical in the production of market-preferred crisp fruit with the optimal conditions. These conditions are reflected in the higher expression of the water transport aquaporins which likely control crispness.