RICE RATOONING - IRRI books - International Rice Research Institute

220 RICE RATOONINGInfected young plants are severely stunted and exhibit uniform yellowing on alltillers. In older plants, symptoms are seen on newly emerging tillers. Numeroustillers are produced at all stages of infection. A week to 10 d after harvest, newsprouts show yellowing in all infected plants. Infected plants produce excessive tillersand fail to produce any grain (2, 19, 30, 32, 42, 43, 49).TRANSMISSIONYellow dwarf is transmitted by Nephotettix cincticeps (10); N. nigropictus (41); N.malayanus (12, 13); N. parvus (11), and N. virescens (47). N. nigropictus and N.virescens are known to transmit the disease in India (37, 44). A blue race of N.virescens is more efficient in transmitting yellow dwarf than the usual green form(38).HOST RANGEYellow dwarf has been transmitted by N. virescens to Alopecurus aequalis, Glyceriaacutiflora, Oryza cubensis (48, 49); O. barathi, O. glaberrima, O. longistaminata, O.minuta, O. nivara, O. perennis, O. punctata, O. rupifogon, O. rupifogon × O.nivara, O. sativa f. spontanea, and Heteropogon contortus (33, 36).VARIETAL RESISTANCEKurosawa (18) first observed varietal reaction to yellow dwarf in the field in Taiwanin 1932. He noted that almost all the Japanese varieties examined after harvest wereseverely infected with yellow dwarf when their tillers grew from the stubble. In fieldtests, Hashioka (4) found considerable differences in resistance or susceptibilityamong 331 varieties tested in Taiwan. Among the varieties tested, 151 varietiesshowed 0-6% infection, 43 showed 7-10% infection, 50 showed 11-20% infection, 32showed 21-30% infection, and 34 showed 41-60% infection. Komori and Takano(17) found that Kaladumai, Loktjan, PeBiHun, Saitama Mochi No. 10, and Tetepwere highly resistant in the field in Japan. Of 70 varieties tested, only Taipei-131,Taipei-310, and No-Lin-49 remained disease free (6).Several cultivars derived from crosses of T(N) 1 × (T 65 × S 705), T 65 × S705, and Wanar 1 × T 65 showed no infection in the main crop and low infection inthe ratoon crop in the field (36). Of 80 varieties/selections tested in the field, 58showed symptoms in the main crop and 77 in the ratoon crop. Twenty-two varietiesshowed no symptoms in the main crop and 3 (MR363, Gamasolu, and HY256)showed no symptoms either in the main crop or in the ratoon crop (Table 1) (33).We screened 106 varieties and breeding lines (including hybrids) for yellowdwarf in the 1984-86 ratoon crop (Table 2, 3). Sixteen lines showed no symptoms inratoon growth. Twenty lines showed less than 2% infection. The lines CT43, CT57,CT1351-1, CT1351-2, Doddabyra, Gangasali, HR35, Intan Mahsuri, lET5975, andKMP104, which did not show infection in the ratoon crop, can be tested in the