Resistance to the South American tomato pinworm Tuta absoluta in high acylsugar and/or high zingiberene tomato genotypes

Zingiberene (ZGB) and acylsugars (AS) are allelochemicals responsible for high levels of arthropod resistance found in Solanum habrochaites (= Lycopersicon hirsutum) var. hirsutum 'PI 127826' and S. (= L.) pennelli 'LA 716', respectively. These accessions were used to develop commercial lines with good levels of pest resistance. The objective of the present work was to assess the ZGB and AS contents and the levels of resistance to Tuta absoluta in tomato hybrids between high ZGB x high AS lines, as compared with their parental lines and with commercial checks. High AS homozygous lines [TOM-688 and TOM-689, both originated from the interspecific cross S. lycopersicum (= L. esculentum) x S. pennelli], high ZGB homozygous lines (ZGB-703 and ZGB-704, both derived from the interspecific cross S. lycopersicum x S. habrochaites var. hirsutum), double heterozygotes for both ZGB and AS, single heterozygotes for ZGB, and single heterozygotes for AS were assessed for AS and ZGB contents. Low-ZGB low-AS checks 'D,bora Max' and 'TOM-684' were used, as well as checks with high ZGB (PI 127826) and high AS (LA 716). The genotypes were submitted to infestation with South American tomato pinworm adults in a screenhouse, and oviposition counts were taken 10 days after the initial infestation date. Plants were scored for overall plant damage and percent leaflets attacked up to the 38th day after infestation. Genotypes heterozygous for ZGB or AS showed allelochemical contents intermediate to those of their high and low content parents, indicating incompletely dominant gene action for contents of each of the allelochemicals. There were no significant differences in T. absoluta oviposition between high-AS homozygous genotypes, high-ZGB homozygotes, single heterozygotes for AS, single heterozygotes for ZGB and double heterozygotes for ZGB and AS, but all these genotypes showed egg counts significantly lower than the low-ZGB low-AS checks. Feeding damage of T. absoluta was higher in the low-ZGB low-AS checks than in any other ZGB-rich or AS-rich tomato genotype. Relative to ZGB or AS single heterozygotes, the heterozygotes for both ZGB and AS showed higher levels of resistance to the insect, as measured by overall plant damage, indicating a synergic effect of the allelochemicals on resistance.