Higher glandular trichome density in tomato leaflets and repellence to spider mites

Abstract

-The objective of this work was to evaluate the feasibility of selection for higher glandular trichome densities, as an indirect criterion of selection for increasing repellence to spider mites Tetranychus urticae, in tomato populations derived from an interspecific cross between Lycopersicon esculentum x L. hirsutum var. glabratum PI 134417. Trichome densities were evaluated in 19 genotypes, including 12 from advanced backcross populations, derived from the original cross L. esculentum x L. hirsutum var. glabratum PI 134417. Counts were made both on the adaxial and abaxial leaf surfaces, and trichomes were classified into glandular types IV and VI, other glandular types (types I+VII), and nonglandular types. Mite repellence was measured by distances walked by mites onto the tomato leaf surface after 20, 40 and 60 min. Spider mite repellence biotests indicated that higher densities of glandular trichomes (especially type VI) decreased the distances walked by the mites onto the tomato leaf surface. Selection of plants with higher densities of glandular trichomes can be an efficient criterion to obtain tomato genotypes with higher resistance (repellence) to spider mites.Index terms: Lycopersicon hirsutum, Tetranychus urticae, 2-tridecanone, methyl-ketone, resistance. Alta densidade de tricomas glandulares em tomateiro e aumento da repelência a ácaros rajadosResumo -O objetivo deste trabalho foi avaliar a eficiência da seleção para maior densidade de tricomas glandulares na resistência (repelência) ao ácaro Tetranychus urticae, em populações de tomate derivadas do cruzamento interespecífico Lycopersicon esculentum x L. hirsutum var. glabratum PI 134417. Foram avaliados 19 genótipos quanto à densidade de tricomas, que incluíram 12 derivados de populações avançadas de retrocruzamentos, obtidos a partir do cruzamento original L. esculentum x L. hirsutum var. glabratum PI 134417. Nas faces abaxial e adaxial dos folíolos, realizaram-se as contagens e os tricomas foram classificados em glandulares tipo IV e VI, outros glandulares (tipo I e VII) e não glandulares. A repelência aos ácaros foi medida pela distância média, percorrida pelo ácaro na superfície do folíolo de tomateiro, após 20, 40 e 60 min. Os biotestes de repelência ao ácaro rajado demonstraram que a alta densidade de tricomas glandulares, especialmente de tipo VI, influencia negativamente a distância média percorrida pelos ácaros na superfície do folíolo. Plantas com número de tricomas glandulares elevado podem ser selecionadas para se obterem genótipos com alto índice de repelência aos ácaros.

Role of allelochemicals and trichome density in the resistance of tomato to whitefly

“…Selected contrasts between groups of genotypes with different allelochemical contents were calculated to characterize possible differences in the degree of pest resistance as a function of allelochemical content. Finally, the pearson' correlation between the number of eggs of B. tabaci biotype B and the glandular trichome density of the tomato plant leaflets was assessed (this density was measured in the previous generation by MALUF et al, 2007). The amount of trichomes is similar to that found by Maluf et al (2007) because we used the same materials, and this analysis merely required counting the trichomes present in the sample, although sampling error may have occurred.…”

“…glabratum specimen PI 134417 (with a high 2-TD content) were used as controls. The following tomato plant lines were also tested: TOM-622 (high 2-TD and low AS and ZGB contents), TOM-687 (high AS and low ZGB and 2-TD contents), ZGB-703 (high ZGB and low AS and 2-TD contents), and nine genotypes obtained by the selffertilization of plants selected by Maluf et al (2007) for the highest glandular trichome densities from two advanced tomato plant populations named BPX-365E and BPX-367C. From the nine genotypes that were selected for trichome density, seven (BPX-365F-751-05-01-03, BPX-365F-751-05-02-02, BPX-365F-751-10-01-01, BPX-365F-751-10-01-02, BPX-365F-899-07-04-02, BPX-365F-899-14-02-03, and BPX-365F-899-14-02-04) corresponded to F7 lines obtained from the crossing of TOM-679 and TOM-600 (from this line, line TOM-622 was selected because it has larger fruits).…”

“…Brazilian tomato plant breeding programs aimed at developing pest-resistant cultivars have adopted the strategy of incorporating resistance alleles from wild specimens containing resistance-related allelochemicals into commercial cultivars (MALUF et al, 2007). Maluf et al (2010) assessed the AS-mediated resistance of the tomato plant to arthropod pests and found that hybrids with intermediate AS contents exhibited satisfactory resistance to Bemisia tabaci biotype B and Tuta absoluta (Lepidoptera: Gelechiidae), similar to homozygous lines with high AS contents.…”

“…These authors found that both allelochemicals were effective in conferring pest resistance in both homozygotes and heterozygotes. Maluf et al (2007) assessed the correlation between glandular trichome density and resistance to the mite T. urticae and found that a high density of glandular trichomes negatively affects the average distance traversed by mites. Therefore, plants with high numbers of trichomes may be selected to develop genotypes resistant to this pest.…”

“…Alth ough correlat ions between the concentrations of foliar allelochemicals (2-TD, ZGB or AS) and the degree of pest resistance have been established (ARAGÃO; DANTAS; BENITES, 2000;MALUF et al, 2007;SILVA et al, 2009;GONÇALVES NETO et al, 2010;MALUF et al, 2010), few critical studies have compared the degree of pest resistance among lines rich in different allelochemicals.…”