Alleviation of cotyledonal cracking in green beans (Phaseolus vulgaris L.) by calcium seed treatment.
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Date
2003
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Abstract
Cotyledonal cracking is a physiological disorder of common beans, and rarely, soybeans
that occurs as transverse fissures across the cotyledons. The phenomenon is generally
referred to as transverse cotyledonal cracking (TVC). Although TVC has been known for
decades now, factors contributing to its occurrence, and how the disorder can be
alleviated, are still not well understood. The objective of this study was to investigate the
effect calcium seed treatment on cotyledonal cracking in green bean (Phaseolus vulgaris
L.) seeds. Six cultivars (Imbali, Sodwana, Outeniqua, Elangeni, Tokai and Tongati) were
examined for water absorption patterns during a 6-h imbibition in distilled water.
Cultivars were categorised according to the rates of water absorption, in the presence of
seed coat, and there was a significant correlation between seed size and water absorption
rate. To examine seed predisposition to TVC, seeds were imbibed with and without seed
coats and TVC was scored every hour for the 6-h duration of imbibition. There was a
significant positive correlation between water absorption rate and TVC. Genetic analysis
of the cultivars using SDS-PAGE revealed that there are possible differences between the
resistant cultivars and sensitive cultivars, with respect to protein patterns. Imbali, one of
the small cultivars (-1.5 g seed -1) that imbibed water uniformly, was resistant to
cotyledonal cracking compared to the largest cultivar (Sodwana -2.5 g seed -1), which
also had a high rate of water absorption. Priming seeds with calcium (CaS04, Ca(N03)2
and CaCl2) osmolarities (0, 1, 10, 50, 100, and 100 mM) increased seed calcium content
and reduced susceptibility to TVC. Comparison of priming and seed coating with respect
to field emergence, TVC, stand establishment and seed yield showed that coating was
better than priming. However, greenhouse studies showed that the effect of priming in the
progeny of treated seeds was significantly better than that of coating, with respect to TVC
reduction. In both laboratory and field studies, it was clear that applying calcium
concentrations greater than 50 mM was not necessary to alleviate TVC and improve seed
performance. Seed germination and emergence were reduced at calcium concentrations
greater than 50 mM. It is concluded that calcium is effective in controlling TVC under
both laboratory and field conditions. The effect of calcium is associated with regulation
of imbibition and improvement of seed calcium content. Enhanced seed calcium content
likely improved cell wall integrity.
Description
Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2003.
Keywords
Beans--Diseases and pests., Beans--Physiology., Green bean., Phaseolus vulgaris., Plants--Effect of calcium on., Seeds--Physiology., Theses--Crop science.