| Abstract |
Tomato, Solanum lycopersicum (Mill.), is one of the most popular vegetables<br/>cultivated in tropical and subtropical regions of the world. In India, it has been cultivated<br/>across an area of 841 thousand ha, with a production of 20.38 metric tonnes (Statista,<br/>2022). However, tomato production is hindered by various abiotic and biotic factors and<br/>among the biotic factors, the polyphagous sucking insect pest, whitefly, Bemisia tabaci<br/>(Genn.) causes both direct and indirect damage and yield loss to the tune of 25-100 per<br/>cent (Mutisya et al., 2016). Both nymphs and adults of B. tabaci feed on phloem sap and<br/>devitalizes the tomato plants and also serves as a vector for the causal organism of tomato<br/>leaf curl virus disease. To manage the whitefly menace in tomato, farmers rely heavily on<br/>chemical insecticides. However, the polyphagous nature of the insect as well as its innate<br/>ability to develop resistance to insecticides makes the management of the pest all the more<br/>difficult. Exploiting host plant resistance could be an alternative tool to manage whitefly<br/>infestation in tomatoes. Thus, the present study entitled “Characterization of resistance in<br/>tomato (Solanum lycopersicum L.) genotypes against whitefly (Bemisia tabaci Genn)” was<br/>undertaken in the Department of Entomology, College of Agriculture, Vellanikkara, Kerala<br/>Agricultural University, Thrissur during 2021-2022.<br/>50 tomato genotypes obtained from different institutes viz., IARI, IIHR, NBPGR,<br/>KAU, TNAU and local collections were screened for whitefly resistance under polyhouse<br/>conditions. The tomato genotypes showed significant variation with respect to eggs,<br/>nymphal and adult populations of whitefly. The mean (pooled) number of eggs per plant<br/>varied between 1.63 and 7.28 eggs/cm2 and within the plants, the highest mean number of<br/>eggs was recorded on the top leaves (8.20 eggs/cm2), followed by the middle leaves (7.40<br/>eggs/cm2), and the bottom leaves (6.30 eggs/cm2). Whereas, the mean (pooled) number of<br/>nymphs per plant varied from 1.45 to 7.41 nymphs/cm2 and within the plant, the highest<br/>number of nymphs was observed on the middle canopy (6.53 nymphs/cm2) followed by<br/>upper (5.84 nymphs/cm2) and bottom (4.62 nymphs/ cm2) parts of the canopy. However,<br/>the mean (pooled) number of adult whiteflies per plant ranged from 1.68 to 7.19 adults/<br/>cm2 and within the plant, the highest number of adults were recorded on the upper canopy<br/>(8.20 adults/ cm2), followed by middle (7.20 adults/ cm2) and the bottom (5.90 adults/ cm2).<br/>Further, the genotypes were categorized based on scale given by Pradhan (1964). Three<br/>genotypes LC Idukki, LC Palakkad and EC 519806 which recorded the mean population<br/>of active stages of whitefly <3.67/ cm2 come under the resistant category, whereas eleven<br/>genotypes with a mean population ranging from 3.67 to 5.57 were categorised as<br/>moderately resistant. Sixteen genotypes were classified under the moderately susceptible<br/>category with a mean population ranging from 5.57 to 7.46, whereas 18 genotypes with a<br/>mean population >7.46 were considered as the highly susceptible category. The leaf area<br/>damage due to the feeding activity of whitefly, which results in the degradation of<br/>chlorophyll was measured indirectly in terms of the hue value of scanned photographic<br/>images of the leaves represented as integrated densities. The tomato genotypes classified<br/>under the resistant category recorded a low hue value ranging from 47 to 53, whereas in<br/>the susceptible genotypes, the hue value reached up to 99.5.<br/>Morphological characters like the type, length and density of trichome, and leaf<br/>lamina thickness were analyzed. Observation of the trichome type revealed that LC Idukki<br/>and LC Palakkad possessed three types of trichome i.e., type IV (glandular), type V (nonglandular),<br/>and VI (glandular). The length of the non-glandular trichome (Type V) present<br/>in the tomato genotypes varied from 513.10 μm to 1475.05 μm. The non-glandular<br/>trichome and glandular trichome densities recorded in the tomato genotypes ranged<br/>between 30.5 to 74.5 per mm2 and 5.50 to 98.00 per mm2, respectively. Leaf lamina<br/>thickness was measured and it ranged from 233.20 μm to 440.5 μm. There was a significant<br/>positive correlation between the whitefly population and the parameters such as nonglandular<br/>trichome density, leaf lamina thickness and length of trichome. However, a<br/>significant negative correlation exists between and glandular trichome density and whitefly<br/>population and it is presumed that the trichome type IV and VI present in the genotypes<br/>confers resistance to whitefly infestation.<br/>The biochemical parameters such as relative leaf water content (91.16 %), and total amino<br/>acid content (3.58 mg g-1) were found to be low, whereas, the total phenol (4.56 mg/ g),<br/>total flavonoid (1.82 𝜇𝑔 gˉ¹), and total alkaloid content (0.59 mg g-1) were significantly<br/>higher in resistant genotype LC Idukki. It was found that there was a significant positive<br/>correlation between the whitefly population and parameters such as relative water content<br/>and total amino acid content, whereas a significant negative correlation was observed<br/>between the whitefly population and parameters such as total phenol, flavonoid and<br/>alkaloid contents.<br/>Based on the present investigation, LC Idukki, LC Palakkad and EC 519806 may<br/>be rated as resistant to whitefly. The studies also show that resistance could be mediated<br/>by the type, density and length of leaf trichomes, along with leaf lamina thickness. It also<br/>indicated that the resistance in tomato to whitefly could be related to biochemical<br/>constituents of the plant, which, however, need to be confirmed. Sustained efforts could<br/>lead to the development of whitefly resistant tomato genotypes, providing the muchneeded<br/>edge to whitefly management in tomatoes. |
