RICE RATOONING - IRRI books - International Rice Research Institute

136 RICE RATOONINGAt the Rice Research Station, Chinsurah (22° 52’N), and Bidhan ChandraKrishi Viswa Vidyalaya, Kalyani (23 °N), experiments were conducted to determinethe possibility of ratoon cultivation for lowland, deepwater areas. This paperdiscusses the results of those experiments.FLOWERING BEHAVIORPhotoperiod-sensitive rice during dry seasonMost of the photoperiod-sensitive rice varieties flower at the end of March or Aprilwhen they are sown in November. The flowering behavior of a few tall, photoperiodsensitivevarieties grown at Chinsurah from 1980 to 1985 showed considerablevariation in heading time. During 1983-84, varieties FR13A, SR26B, Achra 108/1,and Tillakkachari did not flower (Table 1) because of low temperature (9.8-12.9 °C)that prevailed from 22 Feb to 7 Mar. A high degree of flowering stability withvarious photoperiod sensitivity-low temperature interactions is an essential trait fordry-season, photoperiod-sensitive varieties.Ratooned photoperiod-sensitive varietiesSix photoperiod-sensitive, traditional, lowland varieties (NC365, FR13A, Achra108/1, Nagra 41/14, SR26B, and Bansmoti aman) were sown the first week ofNovember 1980. All flowered between late March and early April. Each variety wasratooned at maturity in May. The ratoon crop of FR13A, SR26B, and Achra 108/1showed a burst of flowering in early June. NC365 and Bansmoti aman ratoon cropdid not flower until October. Nagra 41/14 ratoon crop flowered irregularlythroughout the growing period (Fig. 1). All the other varieties showed furthervegetative growth and flowered the third week of October. The same varieties sownin July also flowered during the same period (Table 2).Ratoon of F 2 segregatesThe flowering behavior of F 2 generations of FR13A, Achra 108/1, IR36, and IR50crosses was tested under November sowing and October ratooning.Table 1. Flowering behavior of some lowland photoperiod-sensitive rice varietiesduring dry season, Chinsurah (22°52’N).VarietyFloweringdate1980-81 81-82 82-83 83-84 84-85NC365Bansmoti amanFR13ASR26BAchra108/1TillakkachariBhasamanikNagra 41/14Kumargore28 Mar24 Mar6 Apr4 Apr10 Apr17 Apr–8 Apr7 Apr30 Mar3 Apr8 Apr6 Apr13 Apr17 Apr27 Apr12 Apr5 Apr27 Mar24 Mar3 Apr9 Apr9 Apr12 Apr20 Apr11 Apr28 Mar9 Apr13 AprNFNFNFNF25 Apr14 AprNF25 Mar3 Apr9 Apr7 Apr14 Apr18 Apr––8 AprNF = did not flower.