Factors affecting the efficacy of agar-based substrates for the study of tomato pollen germination

Abstract

SummaryThe present work examines the effects of substrate additions and incubation conditions on in vitro germination of tomato pollen on semi-solid, agar-based substrates with the ultimate aim of defining a standard semi-solid substrate for tomato pollen germination studies. Partial replacement of sucrose by polyethylene glycol (PEG-6000) for osmotic regulation of the substrate significantly increased pollen germination of both the low temperature-susceptible F1 cultivar ‘Dombito’, and the more temperature-resistant cv.‘Supermarmande’, to a level that varied according to the season of pollen harvest. In contrast, partial substitution of sucrose by mannitol was inhibitory to an extent that depended on the final concentration of mannitol in the medium. The optimum pH for germination was 6.5 and the optimum incubation temperature was 15°C. Among the vitamins (riboflavin, thiamine, pyridoxine, niacin, pantothenic acid, p-aminobenzoic acid), amino acids (glutamic acid, aspartic acid), casein hydrolysate, plant growth regulators (gibberellic acid, indole-3-acetic acid, indole-3-butyric acid, indole-3-propionic acid, 1-naphthaleneacetic acid, kinetin) and flavonoids (naringin, myricetin, naringenin, quercetin, rutin) tested, a significant increase in pollen germination was induced only by the flavonoids quercetin and myricetin and, to a lesser extent, by indole-3-acetic acid. In contrast, both kinetin and naringenin were inhibitory, as were both amino acids at 100 mg l–1 and casein hydrolysate (at 1.0 – 10.0 g l–1). On the basis of the above results, we conclude that, for both tomato cultivars tested, the most suitable semi-solid substrate among those examined was that containing 10% (w/v) sucrose, 15.1% (w/v) PEG-6000 and 1.5% (w/v) agar, with the possible addition of 5 mg l–1 quercetin, or 5 mg l–1 myricetin.