Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.16

SPECTROPHOTOMETRIC ANALYSIS OF ANTHOCYANIN REACTION IN POTATO SOLANUM TUBEROSUM (+) S. PINNATISECTUM SOMATIC HYBRIDS AFTER PHTHORIMAEA OPERCULELLA ZELLER (LEPIDOPTERA: GELECHIIDAE) LARVAL FEEDING

S. MUSMECI*, A. LAI**, S. ARNONE*

*) ENEA CR Casaccia, BIOTEC-GEN, Via Anguillarese 301, 00060 Roma

**) Enea C.R. Frascati, FIS – LAS, Via Enrico Fermi 45, 00044 Frascati (Rm)

PTM, anthocyanin, Solanum pinnatisectum, tuber resistance

Potato tuber moth (PTM) (Phthorimaea operculella Zeller) is one of the most important insect pests for this crop. Originated from South American tropical and subtropical areas, it found a suitable habitat in Mediterranean Basin. The larva is mining both leaves and tubers, emphazising its damaging effects especially in Third World Countries, where suitable insect-proof stores for tubers are not available. At the moment, different agronomic and biological control techniques are available in order to reduce the pest impact both in field and in stores, including the use of genetically resistant plants. Natural leaf resistances, conferred by glandular trichomes (Musmeci et al., 1997; Malakar and Tingey, 2000) or leptines (Westedt et al., 1998) have been combined into a unique genotype genetically modified with the gene Cry I (Westedt et al. 1998) expressing Bacillus thuringensis toxin in tubers too. Concerning natural tuber resistance, the wild species S. pinnatisectum shows complete larval resistance (Arnone et al. 1998) and the somatic hybrids S. tuberosum (+) S. pinnatisectum (Menke et al., 1996) demonstrate an intermediate level of resistance (Arnone et al., 1999) to PTM. This resistance could be partially due to glycoalkaloids (Sinden, 1986). However, the breakdown of resistance (from 77,2 % to 38,57 % of larval mortality) on pre-treated tubers at 4 °C and at 38 °C for 4 days, suggests the presence of unstable compounds directly involved in the resistance or related to the inducible defence mechanisms. In addition, during bioassays, an anthocyanin reaction at the preferential larval entrance site (tuber eyes) was always observed. The anthocyanin production, visible at 24 hrs after inoculation, very evident at 48 hrs and increasing with larval feeding, could be related with a direct response of the genotype to specific insect compounds playing the role of elicitors. In fact, preliminary observations showed that the spot formation is induced after a real chewing larval behavior vs. a generic artificial wounding. It is possible to hypothesize that the fast anthocyanin reaction is a plant protective mechanism related to the production of active oxygen species and to limit lipid peroxidation (Baker and Orlandi, 1995). Active oxygen species and lipid peroxidation play a central role in production of plant defence signal molecules (such as salicilic acid and jasmonic acid) against insects and pathogens (Walling, 2000).

In order to better understand the relationship between the anthocyanins, resistance mechanisms and elicitation specificity, bioassays with spectrophotometer (Mancinelli, 1984 modified) have been undertaken in different experimental conditions (antibiosis tests with newly emerging larvae, treatments with larval regurgitant, or artificial scratching). Anthocyanin amount is periodically recorded at 48 hrs and after 6 days, by taking out a tuber tissue carot (ø 5mm h 2mm). Subsequentely, a second check is necessary to record larval mortality and surviving larval weight. The results of this work are presented.