Studies on the bacterial blight disease of rice caused by xanthomonas oryzae (Uyeda & Ishiyama) dowson in Malaysia

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Date
1976-09
Authors
Ban Lee, Ho
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Bacteria blight of rice in Malaysia was shown to be caused by Xanthomonos (Uyeda & Ishiyama) Dowson. The identity of the pathogen was confirmed by cultural physiological and biochemical studies, r.md the fulfillment of l(och's postulates. The disease syndrome was charaterised by three main types of lesions namely streak type, marginal type and spot types. Initially, the symptoms appeared as water-soaked dark green lesions, which later turned yellow, orange or greyist white in colour, with r,ti.nute round yellow bncteriol. beads on lE:sions in the early hours of the morning. The kresek phase of the disease has been recorded. Bacterial blight was found in the three major rice growing area of Malaysia namely Kedah-Perlis Muda area, Seberanc Perai and Krian District in both the main season and off -see.son crcppings. The initial peak outbreaks of the disease were observed in the field as early as the maximum tillering and the milk ripe stage respectively during the growth of the paddy plants. Increased :in nitrogen application ( 120 lbsN/Acre) caused very significant increase in lesion length. Nitrogen application of 80 lhs/acre was found to give moderate infection on a moderately susceptible variety. Jaya:. Phosphorus and potassium had little or no effect on lesion length. Planting space of 8 inches x 8 inches gave the least infection and progressive increase in planting space brought about significant increases :in the disease infection. The sensitive period for disease susceptibility of paddy was found to be between maximum tillering and booting staage.. ... Infections within this period induced maximum disease severity and maximum disease score at tho milk ripe stage with subsequent signiificant yield loss. A yield loss ~assessment technique was proposed using the TJisense Intensity Index which measured the omount of damflc;e on the photosynthetic surface of the po.ddy plants. Yield loss increased with increases in the Disease Intensity Index. Reductions in yield components were relntcd quadratically to the Disease Intonsity Indox .. i-1 Disec-.se IntEmsi ty Inc1ex of 5 and above broueh a re1luction of more thnn 10% losses in yield. i• Yield Loss EstimAtion To.ble w~1s constructed ~md wo.s found useful in foreoRstinc losses due to bcctorial bliGht using Disease Intensity Indices. The multi-prick inoculation technique was developed for mass screening of adult paddy ·variaties for bacterial blight was resistance under field conditions. It/shown to he better than the shenring technique (= clip-inocul0tinn) and the pin-prick technique. Inoculntiono, uc.inc; the mult:i.-pd.cl{ techniqut:, betwoen mnximum tillcring stcge and booting stage and discnse reactions determined ::tt 20 + 2 cinys after inoculation gave the best results. The technique was use. successfully on new paddy genetic lines.
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