Screening of cacao clones for drought tolerance by assessing predawn leaf water potential, growth, and leaf gas exchange

Drought in cacao-producing regions worldwide is causing a decrease in yield and, in severe cases, leading to plant death. This primarily affects small farmers who lack sufficient financial resources or water availability to irrigate their plantations. This study aimed to test 83 cacao clonal genotypes for drought tolerance by evaluating their physiological and morphological features. These genotypes, referred to as drought-tolerant cacao (DTC) genotypes, were selected through mass selection from regions of Bahia, Brazil, severely affected by prolonged droughts. Seedlings of the DTC clonal genotypes and two control clones (CCN 51-drought-intolerant and CEPEC 2002 - drought-tolerant) were obtained from rooted cuttings of plagiotropic branches and evaluated under greenhouse conditions. Three experiments (EXP 1, 2, and 3) were conducted using a randomized block design, with three replications each and two plants per replication of each clonal genotype to test for drought tolerance. Data analyses were conducted using univariate and multivariate statistical analysis. DTC and control clones were subjected to varying soil moisture contents [70, 60, 50, 40, and 30 % of field capacity (FC)] and their controls (maintained close to 100 % of FC) for approximately 40 to 60 days. The results revealed significant statistical differences in growth variables before the plants were subjected to drought. They were categorized based on vigor into three, four, and three groups for EXP 1, 2, and 3, respectively during cluster analysis. DTC and control clones subjected to drought (70, 60, 50, 40, and 30 % of FC) exhibited significant statistical differences in physiological traits compared to the traits of their respective controls (100 % of FC). However, plant growth remained largely unchanged under drought stress (30 or 40 % of FC). DTC clonal genotypes 15, 17, 23, 41, 61, 66, 90, 91, 92, and 93 were more efficient in maintaining net photosynthesis (A) with decreases in soil moisture, showing greater changes only at 40 % of FC. DTC clonal genotypes 14, 32, 41, 61, 69, 70, 88, 89, 92, 95, and 108 maintained stomatal conductance (gs) values similar to those of their controls. Twenty-three DTC clonal genotypes maintained values of A, gs, E, Ci, A/gs, and A/E close to their respective controls, suggesting that these genotypes present features for drought tolerance.