Phenotypic marker in testing TGMS-based hybrids

The thermo-genetic male sterility (TGMS) system of producing hybrid has been proven to work in the Philippines where differences in temperature exists due to elevation, latitude and season. Two TGMS-based hybrids namely, Mestiso 19 and Mestiso 20 released by the NSIC [National Seed Industry Council] are now being commercialized. The fertility/sterility of the female parent is dependent on temperature regimes hence the risk of selfing in hybrid seed production is a possibility. Grow-out test (GOT) is done to evaluate the purity of the parents and F1 hybrid. It is a reliable procedure, however, it takes one full cropping cycle to evaluate samples, hence not practical. At present, only the parents are being evaluated using GOT but not the F1 since the period between harvest and next planting season is short to allow for a GOT. Converting green-base pollen parents into purple-base genotypes (morphological tagging) will facilitate early identification of true F1 hybrids from selfed individuals as early as the seedling stage. Failure in isolation wherein sources of migrant pollen are green-based genotypes can also be detected. Using back crossing method, the pollen parents of Mestiso 19 and Mestiso 20 (TG 101M and TG 102M) were phenotypically tagged with purple coloration on the leaf sheath. Five cycles of back crossing with TG 101M and TG 102M as recurrent parent were done until homozygous phenotypes were obtained. Selection for purple-based individual was done in every back crossing cycle. Test of the backcross genotypes confirmed that purple based are almost identical to the recurrent parent. In terms of combining ability, the new purple based parents were crossed with their respective TGMS parents generating purple-based versions of Mestiso 19 and Mestiso 20. Similarities in agronomic characters such as plant height, tiller number, and maturity were observed. Purple-based coloration was distinctly observed at 21 DAS and was intensified when subjected to mild drought condition.