Screening of rice induced mutants for heat and drought tolerance.

In the Philippines, most rice is currently grown in regions where current temperatures are already close to optimum for rice production. High temperature events greater than 35 deg C have been reported in regions like Cagayan in Region 2 and Nueva Ecija in Region 3 known to be the major rice producing areas in the country. It causes negative impact during the reproductive growth stage, the most sensitive phase affecting anther dehiscence, pollination, and pollen germination, leading to spikelet sterility and thereby reducing grain yield. Mutants are other valuable resources for genetic variations in crop improvement. In the current work, 817 diverse mutants in the M3-M4 generation derived from chemical and physical mutagenesis, anther culture technology and conventional technologies were exploited. They were initially screened for drought stress and leaf blast and the survived lines were further assessed for responses to increased temperatures. To date, promising lines were identified in 2 traditional backgrounds (Ballatinaw and Azucena), 3 modern varieties (PSB Rc72H, PSB Rc4, and IR58), and an introduction (Nipponbare). These materials were exposed to high temperature ranging from 27.1 deg C to 34.4 deg C during anthesis in field trial and screenhouse ranging from 34.0 deg C to 38.0 deg C. Selected heat tolerant mutant lines were identified based on grain fertility in the range of 40-80% and pollen viability ranging from 75-100%. The following were selected: 4 Ballatinaw mutant lines, 2 Azucena, and 2 PSB Rc72 H or Mestizo mutants (Co60); 2 IR58 lines, 27 PSB Rc4, and 3 Nipponbare mutagenized with ethyl methyl sulfonate (EMS) at 2 mg/ml; and 6 AC-derived Nipponbare mutants using anther culture (AC) technology. Phenotyping for drought and heat tolerance, yield, and agronomic evaluation will be further pursued and validated to finally identify high yielding heat tolerant germplasm. Therefore, with these positive mutations, opportunity to develop 'heat proofed' rice resilient to future climate conditions is worth continuing.