Morphological and physiological changes among rice varieties used in the Philippines over the last seventy years

Abstract

Abstract Fifty varieties of rice grown in the Philippines this century were grouped chronologically for comparison in both glasshouse and field experiments at Los Banos. The five groups of lowland, and two of upland, varieties each contained 5 to 11 entries. Plants were grown under three daylengths in the glasshouse experiment. In the field they had to be grown at a relatively low density and nitrogenous fertilizer level. Group comparisons revealed marked changes in growth habit, daylength response and inflorescence characteristics, not always consistently in one direction. Lowland varieties have become shorter, with smaller and more upright leaves and reduced daylength sensitivity. Panicle weight initially became heavier, and then lighter again with greatly increased panicle number. Despite these changes, there has been no change in photosynthetic rate, crop growth rate or kernel weight. However, there has been a marked increase in harvest index and in grain production per day, associated with reduced stature and earlier maturity. Although upland varieties have also become less sensitive to daylength, in other respects they have diverged from lowland varieties towards taller, more sparsely tillering, larger panicle types.