RICE RATOONING - IRRI books - International Rice Research Institute

Morphology and physiologyof ratoon riceB.S. Vergara, F.S.S. Lopez, and J.S. ChauhanInternational Rice Research InstituteP.O. Box 933, Manila, PhilippinesThe morphology of the ratoon plant differs significantly from that of the main cropplant. Usually, plant height (3) is lower and effective tillers (2) are fewer in the ratoonthan in the main crop. However, some ratoon crops have produced more total tillersthan the main crop (2, 33, 37). Ratoon crops also developed many unproductivetillers (3, 10) and axillary buds that continued metabolic activity at the cost of grainfilling.Rice ratooning depends on the ability of dormant buds on the stubble of thefirst crop to remain viable. The buds may be at different stages of development (27)or similar in length (7). Axillary buds that developed at those bud nodes grew intoratoon tillers (Fig. la, b). Tillers regenerated from higher nodes formed morequickly, grew faster, and matured earlier (32). They usually had fewer leaves (1). Thepanicles from ratoons coming from lower nodes produced more grains per paniclethan those from upper nodes, but the fertility percentage decreased (41). Paniclesfrom upper nodes contributed more to ratoon grain yields than those from lowernodes (41).Different varieties produced ratoon tillers differently (43). Some grew tillersfrom all nodes of the stubble, others formed tillers only from lower nodes or mainlyfrom the third node. These findings indicate that ratoon crops will yield well if maincrop stubble is left with 2-3 nodes.Tillers from upper nodes, with high C:N, reacted like old seedlings. Tillersfrom the lower nodes, with low C:N, had young seedling characteristics. Thedevelopment of lower tillers should be encouraged because they resemble youngseedlings (22).In IR44, the lengths of the growing buds did not vary. After 5 d, the bud at thefirst node generally grew faster, followed by those from the second and third nodes(Table 1). Eight days after ratooning, the ratoon tillers began to branch (Fig. la,b).Ratoon tiller development depends on the carbohydrates that remain in thestubble and roots after the main crop is harvested (8, 20, 37). The culm of the riceplant is a vital storage organ. Thick culms may store more carbohydrate than thinculms; this probably would be reflected in ratoon potential.In IR44, culm thickness varied from 2 to 5 mm; most were 3-5 mm thick.Ratoon tillers developed, irrespective of culm thickness. Average tiller productionvaried from 1.33 to 2.90 and was higher for thick culms. Origin and time of tillerdevelopment were not influenced by culm thickness (7).