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Chrislyn A. Drake and John R. Clark

Little research has been done to determine the chilling requirement for southern blackberry cultivars. However, field observations from areas where low amounts of chilling occur indicate that `Navaho' requires more hours of chilling than does `Arapaho'. The objective of the study was to determine a method for measuring chilling requirement using whole plants of two blackberry cultivars, Arapaho and Navaho. One-year-old bare-root plants of `Arapaho' and `Navaho' were field-dug and placed in a cold chamber at 3 °C. Ten single-plant replications of each cultivar were removed at 100-hour intervals up to 1000 hours. The plants were then potted and placed in a greenhouse (daily minimum temperature 15 °C) in a completely randomized design. Budbreak was recorded on a weekly basis. Data for budbreak was analyzed as a two-factor factorial (two cultivars and 10 chilling treatments) by SAS and means separated by lsd (P = 0.05). Data indicated that the chilling requirement for `Arapaho' is between 400 and 500 hours. This is evident as a 6-fold increase, which was the largest increase between two chilling treatments, occurred between 400 and 500 hours. For `Navaho', the largest increase (also 6-fold) occurred between 800 and 900 hours, which indicated a chilling requirement for `Navaho' of 800 to 900 hours. These data support previous observations and indicate the method used was successful in determining chilling requirement for blackberries.

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Chrislyn A. Drake* and James F. Hancock

Black root rot is a serious disease of strawberry (Fragaria ×ananassa Duch.) that causes the death of feeder roots, the degradation and blackening of structural roots, and an overall decrease in plant vigor and productivity. The causal organisms of black root rot are Rhizoctonia fragariae, Pythium sp. and Pratylenchus penetrans (the root lesion nematode). Each organism alone can cause extensive damage to strawberry roots, but studies have shown that black root rot may be more severe when all organisms are present, indicating there is an interaction between the fungal organisms and the nematode. The current method of control for black root rot is methyl-bromide fumigation; however, methyl bromide is to be phased out by 2005, and it is not very effective in perennial matted-row systems. The objectives of the study are to measure levels of tolerance to black root rot in 21 strawberry genotypes. The genotypes were planted in four blocks each of methyl-bromide fumigated and non-fumigated soil, and were evaluated for crown, runner, and inflorescence number; yield; average berry weight; and root health. `Cavendish', `Kent', `Midway' and `Winona' showed the highest degree of tolerance, while `Jewel', `Mesabi', and LH50-4 (a F. virginiana genotype) were the poorest performers.

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Chrislyn A. Drake and John R. Clark

Primocane-fruiting blackberry (Rubus subgenus Rubus Watson) selections have recently been developed by the University of Arkansas, but proper cane-management practices for the new germplasm have not yet been determined. It was observed in previous trials that primocane-fruiting selections flowered and fruited in late July and early August in Arkansas, which is often the hottest part of the summer and earlier than desired. Therefore, this study was conducted to determine the effects of primocane tipping on cane and fruit characteristics and to determine the effect of floricane presence on primocane performance. In Fayetteville, one-year-old plants of selections APF-8 and APF-12 were used to apply the four primocane-tipping treatments in combination with the two cane management treatments (presence or absence of floricanes). In Clarksville, the same genotypes were used to apply the two cane management treatments (presence or absence of floricanes). The tipping treatments had a significant effect on primocane yield and peak harvest as well as other parameters. The cane management treatments had a significant effect on total yield, but no other effects.

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Chrislyn A. Drake and James F. Hancock

Black root rot is a widespread disease of strawberry (Fragaria×ananassa Duchnesne) that causes the death of feeder roots and the degradation of structural roots. The major causal organisms of black root rot include Rhizoctonia fragariae Husain and W.E. McKeen, Pythiumspp. and Pratylenchuspenetrans(Cobb) Filipjev and Schuurmans Stekhoven. The current method of control for black root rot is methyl-bromide fumigation; however, methyl bromide is scheduled to be phased out in 2005, and its effects are short-lived in matted-row systems. The objectives of the study were to measure levels of tolerance to black root rot in 20 strawberry genotypes and to determine which pathogens were present in the soil. The genotypes were planted in four blocks each of methyl-bromide fumigated and nonfumigated soil, and were evaluated for crown number, number of flowers per crown, yield, and average berry weight over two years. The results showed that all three pathogens were present in the field, and that there was a significant genotype × fumigation interaction for yield and crown number in both years. The cultivars Bounty, Cabot, and Cavendish, all released from the breeding program in Nova Scotia, displayed tolerance to the pathogens that cause BRR. Greenhouse studies were conducted using a subset of the genotypes to determine if any one pathogen causes more damage than others, and to determine if susceptibility to a particular pathogen varies between genotypes.