Influence of gamma irradiation on pollen viability, germination ability, and fruit and seed-set of pumpkin and winter squash

The influence of irradiation dose (50, 100, 200 and 300 Gray), irradiation time (July 9th, 11th, 15th, 21st and 28th) and pollen age (0th and 1st days) on the pollen viability, germination ability and fruit and seed-setwere investigated in pumpkin (Cucurbita moschata Duchesne ex Poir.) and winter squash (Cucurbita maxima Duchesne ex Lam.). Along with increasing of irradiation dose, irradiation period and pollen age, pollen viability, germinability and fruit and seed-set decreased, significantly. Irradiated and nonirradiated pollens maintained their viability for 1 - 4 days and 4 - 7 days, respectively. Non-irradiated pollens of winter squash were germinated for 2 days and produced the highest germination rate (22.6 and 22.9%) on July 9th and 11th, respectively. Moreover, irradiated pollens were germinated for 2 days at 50 Gray (1.1 - 8.5%) and for one day at 100 Gray (0.6 - 10.4%). On July 9, the fruit-set rate ranged from75.0% (at 50 Gray) to 63.0% (at 100 Gray) by pollination with 0th day pollens in winter squash. Pollination with irradiated pollens at 50 Gray and 100 Gray gave both seeded and seedless fruits depending on irradiation periods. All fruits obtained from pollinations with non-irradiated pollens were seeded. Although irradiated pollens at 200 Gray and 300 Gray were not germinated in medium, they gave fruit more or less, but fruits were seedless. The highest fruit-set rates were determined 75.0% (57SI21) inwinter squash and 26.3 (55BA01) in pumpkin, pollination with 0th day old pollens. In all irradiation times, the percentage of fruit and seed-set of pumpkin was lower than that of winter squash

Modelling the effect of temperature on seed germination in some cucurbits

The prediction of germination percentage (GP) and germination speed (GS) of the seeds for some cucurbits (watermelon, melon, cucumber, summer squash, pumpkin and winter squash) was investigated by mathematical model based on temperature. The model, D = [a - (b x T) + (c x T2)] of Uzun et al. (2001), was adapted to predict both the GP and GS in relation to 12 different temperatures, namely 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42 and 45°C. In addition, optimum temperature (To = - b / 2 x c) for GP and GS were calculated by using the coefficients obtained from the regression models developed. Observed and predicted optimum temperature (To) for GP and GS varied among species and cultivarsand strong correlations were established between observed and predicted GP and GS based on temperature. The predicted To ranged from 21.6°C (summer squash, pop. Urfa) to 27.8°C (watermelon, cv. Amazon F1) for GP and from 25.5°C (winter squash) to 30.4°C (melon, cv. Hasanbey-1) for GS. These results indicated that predictions based on this mathematical model were highly reliable and that it could be confidently used to predict GP and GS for the evaluated cucurbits

The phenotypic diversity and fruit characterization of winter squash (Cucurbita maxima) populations from the Black Sea Region of Turkey

Winter squash are one of the most important Cucurbit crops in Turkey. Winter squash populations show great diversity in morphological characteristics, particularly fruit length, fruit diameter, fruit shape, fruit brightness, skin thickness , flesh thickness and colour in the Black Sea region of Turkey. In this research, 115 populations of winter squash, Cucurbita maxima Duch, were collected from different provinces of the Black Sea region in 2006 and 2007 and phenotypic diversity in their fruit characters was assessed. The collection showed appreciable phenotypicvariation in fruit shape, fruit colour, fruit brightness, fruit dimension and fruit weight. Cluster and principal component analysis (PCA) were performed to determine relationships among populations and to obtain information on the usefulness of those fruit characters for the definitionof groups. Cluster analysis based on 14 quantitative and 7 qualitative variables identified 10 different groups. The first five principal component axes accounted for 65.0% of the total multivariate variation among the populations. The greater part of variance was accounted for byfruit weight, fruit diameter, fruit length, length of seed cavity and flesh thickness. This evaluation of fruit trait variability can assist geneticists and breeders to identify populations with desirable characteristics for inclusion in variety breeding programs