Acylsugar Contents Research Articles

Helicoverpa armigera management: A review of AVRDC's research on host plant resistance in tomato

Tomato fruitworm (TFW), Helicoverpa armigera (Hübner), is the most destructive pest of tomato ( Lycopersicon esculentum Mill) in South and Southeast Asia. Research was initiated at AVRDC in 1980 to identify sources of resistance to this pest and to breed TFW-resistant tomato lines suitable for the region. Germplasm screening revealed high levels of TFW resistance only in the wild Lycopersicon species, particularly L. hirsutum and L. pennellii. Consequently TFW resistance breeding research focused on introgressing resistance from the wild species into the cultivated tomato. In the first resistance breeding efforts from 1981 to 1988, L. hirsutum accessions 76W-PI134417-A and 77W-PI134417-1 were selected as donor parents in a backcrossing program with L. esculentum. Backcross lines with significantly lower pest damage were derived from this program but all were invariably small-fruited and not commercially acceptable. From 1988 to 1995, a second attempt was undertaken using L. pennellii accession LA 716 as the resistance donor parent. Selection of resistant progenies was based initially on TFW damage and subsequently on acylsugar content, the compound that confers insect resistance, in leaves. We failed to find backcross progenies with acylsugar levels near that of the donor parent. Furthermore, progenies with higher acylsugar levels also showed low pollen production and other undesirable horticultural traits. From 1994 to 1996, in collaboration with Cornell University, an attempt was made to introgress the fruitworm resistance genes from LA 1777 ( L. hirsutum f. typicum) using QTL mapping. However, none of the near isogenic lines carrying individual L. hirsutum introgressions associated with fruitworm resistance showed resistance. Our research demonstrated the presence of high levels of TFW-resistance in several wild tomato accessions but our efforts to introgress this resistance into the cultivated tomato in order to combine it with acceptable fruit qualities did not succeed. Future of such classical breeding approach is discussed.

Does Host Plant Chemistry Influence Feeding and Ovipositional Behavior of Fruitborer in Tomato?

ABSTRACT The tomato fruitborer (TFB), Helicoverpa armigera Hub., is one of the most difficult pests to control with insecticides. Development of cultivars that are resistant to this insect has become an important strategy in management. Resistant/tolerant accessions of tomato (Lycopersicon esculentum Mill.) to TFB have been identified based on feeding and ovipositional behavior of TFB. The moths laid more eggs on accessions LE 4 (52 eggs/plant), LE 104 (73) and LE 281 (57) than on LE 355 (11). Biochemical assays indicated that the acylsugar contents in leaves of tomato accessions varied from 38 to 266 nmol/cm2. High acylsugar content was negatively associated with number of eggs laid/ plant (r = -0.94). Content of alpha-tomatine in fruit varied from 0.57 to 3.51 mg.g−1 of fresh tissue. The alpha-tomatine concentration was weakly, and negatively, associated with percent fruit damage by TFB (r = -0.39). The fruit pigments lycopene and carotene influenced the feeding of TFB as there were differences in feedi...

Variation in tomato host response to Bemisia tabaci (Hemiptera: Aleyrodidae) in relation to acyl sugar content and presence of the nematode and potato aphid resistance gene Mi.

Two commercial cultivars of tomato, Alta and Peto 95, the accession line number LA716 of Lycopersicon pennellii and lines 94GH-006 and 94GH-033 (backcrosses between Peto 95 and LA716), with different leaf acyl sugar contents were screened for resistance to Bemisia argentifolii Bellows & Perring (corresponding to the Spanish B-biotype of Bemisia tabaci (Gennadius)), in greenhouse- and field-no-choice experiments. There was no oviposition on LA716 (with the highest acyl sugar content) while the greatest fecundity and fertility values were observed on the cultivar Alta (no acyl sugar content). However, no clear relationship was found between the low acyl sugar content in the other tomato cultivars tested and whitefly reproduction. Thus, resistance to B. tabaci did not appear to correlate with acyl sugar content below a threshold level of 37.8 microg cm-2 leaf. In a greenhouse choice-assay, B. tabaci exhibited reduced host preference and reproduction on the commercial tomato cultivars Motelle, VFN8 and Ronita all of which carry the Mi gene resistance to Meloidogyne nematodes and the aphid Macrosiphum euphorbiae (Thomas), than on the Mi-lacking cultivars Moneymaker, Rio Fuego and Roma. When data of Mi-bearing plants were pooled, the mean values for daily infestation and pupal production of B. tabaci were significantly lower than those of Mi-lacking plants. This reflected a level of antixenosis- and antibiosis-based resistance in commercial tomato and indicated that Mi, or another closely linked gene, might be implicated in a partial resistance which was not associated either with the presence of glandular trichomes or their exudates. These findings support the general hypothesis for the existence of similarities among the resistance mechanisms to whiteflies, aphids and nematodes in commercial tomato plants.