Precise selection of superior Hevea genotypes from 2014 hand-pollinated progeny

The hybridization and selection in rubber (Hevea brasiliensis) aim to produce superior genotypes. The perennial nature of Hevea is the major limitation in rubber breeding. Early selection is crucial for strengthening and shortening the breeding program. Therefore, 20 randomly selected individuals of the 2014 hand-pollinated progeny were used for the current morphological, anatomical, biochemical, and gene expression study to identify superior genotypes for future recommendations. The average yield, girth, and bark thickness were measured as morphological characteristics, while sucrose, inorganic phosphorus, thiol, and polyphenol were measured as biochemical characteristics. Dry rubber and total solid content were also measured as diagnostic indicators of latex. The bark anatomical analysis was done with a modified staining protocol. Gene expression analysis was performed using the Catalase (HbCAT) and Superoxide dismutase (HbSOD) genes to evaluate the proneness for Tapping Panel Dryness (TPD). Results indicated that girth (79.8%), bark thickness (60.8%), bark anatomical parameters such as the diameter of latex vessels (60.1%) and the number of latex vessels per unit area (density) (89.2%) positively correlated with rubber yield. The genotypes 2014HP-11, 2014HP-42, 2014HP-78, 2014HP-25, 2014HP-102, 2014HP-35, 2014HP-39, and 2014HP-21 showed comparatively higher morphological characteristics. The genotypes 2014HP-56 and 2014HP-57 showed potential for stimulation due to their high sucrose and low inorganic phosphorus contents. All other genotypes showed below-average performance for commercial recommendations. The optimized bark anatomical screening protocol of the current study clearly stained the secondary latex vessels. Genotypes 2014HP-21 and 2014HP-98 showed higher TPD traits morphologically. Therefore, expression of HbCAT and HbSOD genes was tested. The fold difference value was upregulated in the genotypes 2014HP-21 and 2014HP-98. As a result, these two genotypes are possibly prone to TPD. In conclusion, this study optimized the bark anatomical screening protocol, identified promising high-yielding genotypes and pinpointed the possible vulnerability of two genotypes (2014HP-21 and 2014HP-98) to TPD.