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Ganesh R. Panta, Lisa J. Rowland and Ganesh R. Panta

Dehydrins are major plant proteins that increase with cold or drought. Using a previously identified 2.0-Kb blueberry dehydrin cDNA, additional dehydrin clones were isolated and characterized. Experiments were conducted to determine effect of drought and cold treatment on dehydrin gene expression in several blueberry cultivars. Besides previously characterized 65, 60, and 14 kDa dehydrins in floral buds additional less abundant dehydrins were observed in stem and root tissues. The same major dehydrins were induced by both drought and cold stress but at different levels. Dehydrin expression was positively correlated with cold and drought tolerance. In addition, photoperiod was observed to affect dehydrin expression. Dehydrins were induced to higher level in cold treated plants kept in total dark than in plants kept at a short photoperiod of 10 hours of light/14 hours dark.

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Ganesh R. Panta, Mark W. Rieger and Lisa J. Rowland

The blueberry industry experiences significant losses every year due to environmental factors with a dehydrative component, such as drought and freezing stress. In a recent survey of blueberry research and extension scientists in the United States, lack of cold hardiness and susceptibility to spring frosts were identified as the most important genetic limitations of current cultivars. For these reasons, cloning and characterization of expression of dehydration-responsive genes (dehydrins) have been ongoing in our laboratory. To date, one full-length (2.0 kb bbdhn1 gene) and four partial-length dehydrin cDNAs have been cloned and sequenced. Very high homology at the DNA and protein levels were found among the blueberry dehydrin clones, particularly at the 3' ends. From DNA blots, it appears that blueberry dehydrins are encoded by about three genes with high homology to the full-length 2.0 kb bbdhn1 cDNA clone and a few other less related genes. The 2.0 kb bbdhn1 gene was mapped in a blueberry population segregating for cold hardiness and chilling requirement. Expression studies indicated that dehydrins are induced by cold and drought stress. In general, dehydrins were induced in all organs examined in response to cold stress, including floral buds, leaves, stems, and roots. Under drought conditions, dehydrins were induced primarily in stems and their levels declined in roots. Some of the induced dehydrins were the same for drought and cold stress, whereas others were unique to a given stress. Levels of dehydrin accumulation correlated positively with cold hardiness; however, levels of dehydrins did not correspond precisely to the degree of drought avoidance.

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Rajeev Arora, Lisa J. Rowland, Ganesh R. Panta, Chon-Chong Lim, Jeffrey S. Lehman and Nicholi Vorsa

Mode of inheritance of cold hardiness (CH) in woody perennials is not wellunderstood. This study was undertaken to determine the mode of inheritance and gene action of CH in blueberry (Vaccinium section Cyanococcus). Two testcross populations (segregating for CH) derived from interspecific hybrids of V. darrowi (drw) × V. caesariense (csr) were used. Plants were cold-acclimated by a 4-week exposure to 4°C. Bud CH (LT50) was defined as the temperature causing 50% injury (visual) when subjected to controlled freeze–thaw. Results show that the drw and csr parents had an LT50 of –13° and –20°C, respectively. The F1 population exhibited mean LT50 of –14.7°C. The csr and drw testcross populations had a mean LT50 of –18° (39 individuals) and –14°C (33 individuals), respectively. Individuals of each population were distributed between parental values with center of distribution skewed toward the testcross parent. Since individuals having LT50s as same as the recurrent parents were present in each population of only 33–39 plants, data suggest that CH is determined by relatively few genes. To determine gene action, the estimates for various genetic parameters (calculated from joint scaling test) were used in generation means analysis to test various models. Results indicate that CH in blueberry can be best explained by simple-additive dominance model, whereas models including epistatic components did not satisfactorily explain the data.

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Lisa J. Rowland, Elizabeth L. Ogden, Rajeev Arora, Chon-Chong Lim, Jeffrey S. Lehman, Amnon Levi and Ganesh R. Panta