Physiological responses to drought and experimental water deficit and waterlogging of four clones of cacao (Theobroma cacao L.) selected for cultivation in Venezuela

Abstract

Cocoa is sensitive to both water deficit (WD) and waterlogging (WL), especially during the juvenile stage. The aim of this study was to compare in four cocoa clones the water status, gas exchange and photochemical activity of PSII of adult trees subjected to natural drought in the field, and young individuals in the greenhouse subjected to either WD or WL. In the greenhouse, pots in which eight-month-old saplings were growing were placed in 8-L plastic buckets and either weekly watered (control, C), left without watering (WD), or filled with tap water up to 1cm above soil surface (WL). In the field, drought affected clones differently in their water relations and photosynthetic responses. In the greenhouse, after 35 days of treatment, the four clones showed decreases in water potential which were stronger under WD than WL. Photosynthetic rate (PN) decreased on average 86% due to WD and 60% due to WL, clone 415 being the most susceptible to both stresses. On average, PN reached 100% of control values ​​7 d after re-watering but only 74% after drainage. Stomatal closure with maintenance of leaf water was the general response to WD. Clone 439, with highest relative lenticel area, was the one in which PN recovered most from WL. Lenticel hypertrophy, particularly in clone 439, apparently was one of the mechanisms of acclimation to WL. Chronic photoinhibition occurred in no case. We conclude that all clones are adequate for growth in the field, although 415 is the one with lower PN during the rainy season. Saplings of all clones are suitable for cultivation in drought-prone areas for dry periods of at least a month, and clone 439 is the one best suited for soils under short-term WL .