Symptom Identification and Control Methods of Rice Dwarf Disease

The symptoms are mainly distributed in the southern rice-growing areas. Also known as rice common dwarf disease, common dwarf, green dwarf, etc. After rice is infected from the seedling stage to the tillering stage, the plant becomes dwarfed, tillering increases, leaves are dark green and stiff, and in the later growth stage the diseased rice cannot head or set grain. Diseased leaf symptoms manifest as two types. In the white-spot type, dashed-line-like yellowish-white dotted streak spots parallel to the leaf veins appear on the leaves or leaf sheaths, most obvious at the base. The new leaves above the first diseased leaf all show dotted streaks, while the older leaves below generally do not. In the twisted type, under insufficient light conditions, the heart leaf emerges twisted, and as the heart leaf extends, wavy notches appear on the leaf margins, and the color is pale yellow. When the disease occurs at the booting stage, white dotted streaks mostly appear on the flag leaf blade and leaf sheath, the panicle neck shortens, forming an enclosed or semi-enclosed neck panicle.

The pathogen Rice dwarf virus, abbreviated RDV, is called rice dwarf virus and belongs to the plant reovirus group of viruses. The virus particles are spherical polyhedra, isometric and symmetrical, with a size of 75 nm, and the particles contain double-stranded ribonucleic acid. The inactivation temperature of the virus is 40-45°C, the dilution endpoint is 1000-100000 times, and the in vitro survival period is 48 hours. The virus particles are mostly concentrated in the chlorotic parts of diseased leaves. In the leaf cells of the white spots, nearly spherical X-bodies containing empty vacuoles are present.

Transmission route and disease conditions This virus can be transmitted by the green rice leafhopper, the two-striped green rice leafhopper, and the electric-light leafhopper. The green rice leafhopper is the main vector. Viruliferous leafhoppers can transmit the virus for life and can transmit it through eggs. The minimum acquisition time for the green rice leafhopper to acquire the virus by sucking on diseased rice is minutes. After acquiring the virus, a circulation period is required before it can transmit the virus; the circulation period is 17 days at 20°C and 12.4 days at 29.2°C. After rice is infected, symptoms appear after an incubation period; at the seedling stage with a temperature of 22.6°C, the incubation period is 11-24 days, and at 28°C it is 6-13 days. The incubation period is short when infection occurs from the seedling stage to the tillering stage, and thereafter lengthens with increasing age. The virus overwinters in the body of the green rice leafhopper, and the green rice leafhopper overwinters in the nymph stage on short-awned foxtail, emerges as an adult the following spring and migrates back to rice fields to cause damage. After the early rice is harvested, it migrates to late rice to cause damage. After the late rice is harvested, it migrates to short-awned foxtail, winter rice, and 38 other grass family plants to overwinter. The number of viruliferous insects is the main factor affecting the occurrence of this disease. Rice is more susceptible before the tillering stage. Warm winter and spring and drought in summer and autumn favor the disease. Tender rice seedlings and abundant insect sources lead to severe disease.

Control methods (1) Select resistant (tolerant) varieties such as International 26, etc. (2) Plant in contiguous blocks to prevent leafhoppers from transmitting the virus on early and late rice and varieties with different maturity traits. Harvest early rice early to avoid insect sources migrating into late rice. When harvesting, face away from the late rice. (3) Strengthen management to promote early development of rice seedlings and improve disease resistance. (4) Promote chemical weeding to eliminate weeds such as short-awned foxtail and reduce overwintering insect sources. (5) Control insects to prevent disease. Timely control the first-generation nymphs reproducing in rice fields, and grasp the peak period of green rice leafhopper migration to double-cropping late rice seedling fields and main fields to eliminate insect sources before virus transmission. Options include 25% buprofezin wettable powder, 25 g per 667 sq m, or 35% suishijing emulsifiable concentrate 100 ml, 25% metolcarb wettable powder 100 g, diluted with 50 L of water and sprayed, once every 3-5 days, for 1-3 consecutive applications.