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Roberto Santos, Bradley H. Taylor and Roger Kjelgren

The effect of root pruning on shoot length and water relations of `Bellaire' peach was investigated as a means of controlling vegetative growth. On 27 April, 25 May, and 23 June, 1990, five-year-old trees were root pruned to a 0.35 m depth at either 0.4 or 0.8 m from the tree trunks along both sides of the row. Shoot growth was measured biweekly through the growing season, and the diurnal pattern of stomatal conductance and water potential was followed in late June, July, and August. Stomatal conductance of the root-pruned treatments was less than the control, while there were no differences in water potential among treatments. Reduced shoot elongation was evident within a month of root pruning at 0.4 m for all timing treatments, but at 0.8 m it varied with the date of pruning. The first root pruning at 0.4 m reduced cumulative shoot elongation 39% compared to the un-pruned control trees, while the remaining treatments reduced it 14%. While root pruning limited cumulative shoot elongation in all treatments, the earliest 0.4 m treatment was most effective, possibly due to pruning of a larger percent of the root system prior to rapid shoot elongation. Stomatal closure in root-pruned trees appeared to moderate diurnal water deficits at levels similar to the control.

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Giuseppe Reforgiato Recupero, Giuseppe Russo, Santo Recupero, Roberto Zurru, Bruno Deidda and Maurizio Mulas

In 1968, the CRA-Research Center for Citriculture and Mediterranean Crops (CRA-ACM) started a research program aimed at breeding citrus rootstocks. The monoembryonic species C. latipes (Swing.) Tan. was used as the female parent; trifoliate orange [Poncirus trifoliata (L.) Raf.], sour orange, and volkamer lemon (C. volkameriana Pasq.) were used as male parents. The behavior of some of these hybrids tested with other standard rootstocks in Sicily and Sardinia was evaluated. The cultivars under comparison included ‘Washington’ navel orange and ‘SRA 92’ clementine in Sardinia and ‘Tarocco’ orange in Sicily. Our results showed the dramatic influence of rootstock on plant growth and yield; only minor effects on fruit quality were observed. Among the standard rootstocks tested, Swingle citrumelo provided the highest yield. Some of the tested hybrids (F5 P12, F6 P12, and F6 P13) may improve plant yield, thus maintaining good fruit quality. Encouraging data obtained with these hybrids may justify the use of monoembryonic species of the Papeda subgenus for breeding citrus rootstocks.

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Sindynara Ferreira, Luiz Antonio A. Gomes, Wilson Roberto Maluf, Vicente Paulo Campos, José Luiz S. de Carvalho Filho and Daniela Costa Santos

This study assessed the reaction of dry bean and snap bean cultivars to infection by Meloidogyne incognita (races 1, 3) and by Meloidogyne javanica, two species of root-knot nematodes. Three independent experiments were done, one for each species or race of Meloidogyne, using randomized complete block designs with four replications (plots) and four plants per plot. A plot with the susceptible tomato cultivar Santa Clara was used in each block to determine the efficiency of the inoculum and to calculate the reproduction rate for each of the genotypes assessed. The bean cultivars Aporé and Talismã were highly resistant to Meloidogyne javanica, slightly resistant to Meloidogyne incognita race 1, and moderately resistant and slightly resistant, respectively, to Meloidogyne incognita race 3. The snap bean cultivars Macarrão Atibaia and Macarrão Preferido were slightly resistant to Meloidogyne javanica and moderately resistant and susceptible, respectively, to Meloidogyne incognita race 1. The reactions of the latter cultivars against Meloidogyne incognita race 3 were very resistant and slightly resistant, respectively. The results of these experiments showed that the dry bean cultivars Aporé and Ouro Negro and the snap bean cultivar Macarrão Atibaia have potential to be used in breeding programs for a broader spectrum of root-knot nematode resistances.