An adventure in applied science - IRRI books - International Rice ...

Early research and training results 105One of the characteristics the breeders were trying to introduce into improvedvarieties was that of seed dormancy so that the grains would not sproutin the panicle when a prolonged rainy spell came at harvest time. On the otherhand, when the breeders wanted to get three generations a year, they neededto break dormancy soon after harvesting so that the seed from one generationcould be planted immediately. Jennings worked on the problem and soonfound that if dormant seed was placed in an oven at a temperature of 50 °C for4-5 days, dormancy would be broken in most varieties (a few of the moreobstinate ones required as much as 10 days).Jennings conducted a series of studies on the technique of bulk breedingmethods when (as in most of IRRI's early crosses) tall and short plants werecrossed. He believed that the bulk method was advantageous for reasons ofeconomy, easy management, low labor costs, and ease of record keeping.However, he felt that superior selections could not be made when tall plantswere left to compete with short ones, because the latter would suffer fromshading. He demonstrated this in field studies and showed that the bulkmethod was highly satisfactory if the tall plants were removed as soon as theybegan to flower. This left the short plants to compete among themselves andsuperior individuals were selected.Jennings attributed much of the slow progress in bulk breeding in Asia tothe fact that plant breeders did not realize that the varieties with the highestyield potential were the short ones, these being the varieties that either wereeliminated or appeared weak and unproductive because of the competition forlight that the tall varieties gave. Much of IRRI’s breeding work utilized thismodified bulk breeding method in the early generations; later generationswere then grown in pedigree rows for final selection or rejection.In 1963-64, Chang devoted considerable effort to studying the inheritanceof quantitative characters when tall indicas were crossed with short. He usedas his principal cross Peta (180 cm tall) and I-geo-tse (100 cm). He concludedthat there were no genetic barriers to selecting from the F 2 generation onwardprogeny that combined the desirable morphological traits of short stature,short and erect leaves, early maturity, and adequate number of panicles.Chang also investigated the degree of sterility in japonica-indica crosses, aswell as the cytological evidence for such sterility. He studied the inheritanceof photoperiodism and of resistance to the rice blast disease and the impact ofnitrogen levels and spacing on yield components such as panicle number,number of grains per panicle, and grain weight. All this information helpedbuild a sound scientific basis for the breeding program.Another development to assist the effort occurred in mid-1964, whenBeachell set up a rice grain quality laboratory in the service building so thathundreds of samples from the breeding program could be processed quickly.By the end of 1964, 7,000 samples had passed through the laboratory. The datacollected included milling percentage and grain size, shape, translucency, andchalkiness. Cooking quality was based on an alkali digestion test that measuredgelatinization temperature and an iodine blue test that reflected the