Salinity Stress and Varietal Resistance in Rice: Effects on Whitebacked Planthopper

Abstract

Plants grown under physicochemicai stresses frequently become more susceptible to insects. We determined the effects of salinity stress at 1.0 and 1.2 S/m electrical conductivity on the magnitude and expression of resistance of rice (Oryza sativa L.) cultivars to So&atella furcifera (Horv~th) under glasshouse conditions using natural daylight of 12 h, 29/21 °C (day/night), and minimum 70% relative humidity. Salinity stress increased N, decreased K, and decreased the quantity of allelochemicals extracted as steam distillates from rice plants. Intake and assimilation of food, growth, adult longevity, fecundity, and population increase of the insect were significantly greater on plants grown at salinity level of 1.2 S/m than on unstressed control plants. Regardless of the level of stress, the difference between susceptibility of 'Taichung Native 1' (TN1) and resistance of 'IR2035-117-3' (IR2035) cultivars remained distinct. Painting of steam-distillate extract of resistant IR2035 plants on susceptible TNI plants made them less attractive and decreased food intake and assimilation by S. furclfera. In contrast, intake and assimilation of food increased significantly on IR2035 plants painted with TNI extract. Effects of physicochemical stresses, such as salinity, must be considered when breeding insect-resistant rice cultivats for salinity-prone areas. R ICE IS CULTIVATED under diverse climatic, hydrological, and edaphic conditions. The stability of rice production frequently is threatened by increases in pest incidence and the prevalence of physicochemical stresses, including salinity. Several species of insects affect the rice crop in South and Southeast Asia. Of these, the whitebacked planthopper is a major pest in Fiji, Japan, Korea, Vietnam, Thailand, India, and Pakistan (Khan and Saxena, 1986a). Under favorable conditions, the insect produces several generations per crop and inflicts heavy damage due to hopperburn (Pathak, 1968). In South and Southeast Asia, nearly 60 million ha of land are affected by salinity ranging from 0.4 to 1.8 S/m (Akbar, 1986). Higher levels of salinity are a major obstacle to high-grain yields on about 27 million ha of land in deltas, estuaries, and coastal fringes in Asia. These areas are physiographically and climatically suited to rice production, but grain yield is reduced drastically at salinity level of 1.0 S/re. Highyielding, semidwarf cultivars, which lack tolerance to salinity, are grown in inland saline areas, but lowyielding, salt-tolerant, traditional, tall 'indica' rices with long growth duration are cultivated in coastal saline environments (Akbar, 1987).

Crop Loss Assessment in Rice

“…Yield is determined from the integration of climate and soil resources with biological and genetic performance under a given level of management. Abiotic factors such as nutrient deficiencies or soil toxicities may make the plant more vulnerable to pest damage by reducing the plant's ability to resist pest attack (Salim et al 1990). High fertility, however, may allow greater tolerance of damage (Singh and Singh 1977).…”

Seleção de genótipos de arroz tolerantes à salinidade durante a fase vegetativa

“…Uma das alternativas para contornar esse problema é a seleção de genótipos mais tolerantes à salinidade nos estádios de germinação e estabelecimento da plântula. Na literatura, já existem estudos a respeito do efeito da salinidade nos diferentes estádios de desenvolvimento de plantas de arroz (CAMPOS & ASSUNÇÃO, 1990;SALIM et al, 1990;AHMED & GUPTA, 1991;YAN & TAN, 1991, YEO et al 1991LUTTS et al, 1996), havendo, no entanto, a necessidade de outras pesquisas que visem à identificação de genótipos tolerantes à salinidade. Em cultivos de arroz efetuados em solos com condutividade elétrica entre 1,4 e 25,6dS m -1 , GORE & BHAGWAT (1988) verificaram uma redução na altura de planta, produção de perfilhos e produtividade.…”

“…As variáveis condutividade elétrica do extrato saturado do solo e nota de vigor no 17 o e 27 o dia apresentaram diferenças apenas para salinidade. A nota de vigor no 27 o dia e taxa deDHAMASRI (1989),SALIM et al (1990),YAN & TAN (1991),YEO et al (1991) e FAGERIA (1991. Estudos realizados porMARASSI et al (1989), em 81 cultivares e nove linhagens locais de arroz para tolerância à salinidade, mostraram que os materiais eram mais tolerantes na fase reprodutiva que na vegetativa e que a altura de planta e comprimento da panícula correlacionaram-se fortemente com a salinidade a 8 dS m -1 .…”

Silicon-based Fertilizer Applications Have No Effect on the Reproduction and Development of the Citrus Mealybug, Planococcus citri Risso (Hemiptera: Pseudococcidae), Feeding on Fiddleleaf Fig, Ficus lyrata (Warb.)

“…Citrus mealybugs have piercing-sucking mouthparts, which are used to remove fluids from the phloem sieve tubes. Silicon-based fertilizer applications have been demonstrated to inhibit the feeding of piercingsucking insects (Salim and Saxena, 1992;Salim et al, 1990;S ogawa, 1982) and stem borers (Djamin and Pathak, 1967;Nakano et al, 1961;Sasamoto, 1961;Ukwungwu, 1990).…”

“…Currently, there is minimal quantitative information associated with the use of silicon in preventing outbreaks of insect and/or mite pests of dicot plants grown in greenhouses. A number of studies have correlated increased silicon content in monocot plants such as rice and maize (Zea mays L.) with enhanced insect resistance (Djamin and Pathak, 1967;Moore, 1984;Rojanaridpiched et al, 1984;Salim and Saxena, 1992;Salim et al, 1990;Sharma and Chatterji, 1971;Sujatha et al, 1987;Ukwungwu, 1990). Moreover, additional studies have correlated applications of silicon-based fertilizers (as growing medium amendments or drenches) with increased insect resistance (Gomes et al, 2005;Moore, 1984;Sétamou et al, 1993;Wadham and Parry, 1981).…”