Search Results

You are looking at 1 - 10 of 10 items for

  • Author or Editor: M. Cohen x
Clear All Modify Search

Tomato yellow leaf curl virus (TYLCV), transmitted by the tobacco whitefy (Bemisia tabaci Genn.), can be devastating to tomato (Lycopersicon esculentum L.) crops in tropical and subtropical regions. The development of resistant cultivars is the best option for control of TYLCV. However, all the available resistant commercial cultivars tested at the Volcani Center, when inoculated with TYLCV, developed different levels of disease symptoms. In this study, we report the development of a breeding line, TY172, which is a symptomless carrier of TYLCV. Line TY172, whether infected in the greenhouse with viruliferous whiteflies, or when grown in the field under natural infection, showed no symptoms of the disease. Viral DNA was detected in infected TY172 plants, albeit at much lower levels than a susceptible infected control. In addition, grafting experiments using infected susceptible scions grafted onto TY172 stocks, showed that even when exposed continuously to very high levels of virus, line TY172 did not develop disease symptoms, nor did it accumulate high levels of the virus. When TY172 was crossed with susceptible lines, the hybrids exhibited milder symptoms and lower viral content than the susceptible parent, yet higher than that of TY172, suggesting a partial dominance for the TY172 resistance. Upon inoculation of F2 populations, the amount of symptomless individuals appeared in a ratio of≈7:64. This suggests that at least three genes may account for the resistance.

Free access

Abstract

The presence of tristeza in Israel has prompted an interest in inarching citrus trees grafted on sour orange (C. aurantium L.) or Palestine sweet lime (C. limettoides Tan.) rootstocks. Tests conducted since 1976 at several locations in Israel have shown that: a) Swingle citrumelo (C.P.B. 4475) [C. paradisi Macf. × P. trifoliata (L.) Raf.] outperforms other rootstocks when used for inarching citrus trees; b) Swingle inarches of small diameters grow faster than those of large diameter; c) inarches on young trees grow faster than those on older trees; and d) the effect of Swingle citrumelo, C. volkameriana, and, to a lesser extent, of sour orange on ‘Shamouti’ fruit quality are similar to their effect when used as rootstocks.

Open Access

Petunia vein clearing virus (PVCV), a possible member of the caulimovirus group, was detected in several cultivars of vegetatively propagated petunias (Petunia ×hybrida Hort. Volm.-Andr.) grown in commercial nurseries. Leaf dip preparations and ultrathin sections of leaf tissue were analyzed by transmission electron microscopy (TEM). Spherical virus particles, 45-50 nm in diameter, were observed in samples taken from symptomatic petunia plants. The virus was purified and a polyclonal antiserum was prepared. In immuno-specific electron microscopy (ISEM), the PVCV antiserum-treated samples reacted with a distinct decoration on the virus suspect particles. A polymerase chain reaction (PCR)-based assay was used to detect PVCV in total nucleic acid extracts derived from infected petunia plants. Two primer pairs were designed to flank a 736-base-pair sequence located in the RNA-dependent RNA polymerase gene of the PVCV genome. A DNA fragment of predicted size was visualized in agarose gels. The authenticity of the amplified DNA fragment was confirmed by restriction analysis and by hybridization with the virus-specific PVCV DNA probe. The virus could be detected efficiently in high dilutions of sap extracted from infected petunia plants.

Free access

Peach [Prunus persica (L.) Batsch] cDNA libraries have been constructed from RNA isolated from immature (30 days after bloom) and ripe fruit. cDNA clones of interest have been identified by differential hybridization among the cDNAs of various peach cultivars or from several stages in fruit development. In addition, several clones were isolated by low stringency hybridizations with oligonucleotides derived from a tomato polygalacturonase cDNA sequence and a cucumber peroxidase amino acid sequence. The pattern of accumulation of the corresponding mRNAs during fruit development was examined by RNA gel-blot analyses in the commercial cultivar Suncrest. Three cDNA clones, pch201, pch307, and pch313, were related to mRNAs that accumulate during the softening stage of fruit development. cDNA clones pchl03, pch205, and pch306 were related to an mRNAs that increase in abundance throughout development, with maximum levels in ripe fruit. cDNA clones pch104 and pch202 were related to mRNAs that exhibit maximum abundance in midfruit development, and clone pch108 was related to mRNA that decreases as the fruit matures. Southern analyses indicated that seven of the cDNAs are represented by only a few genes, while pch104 detects a repetitive family, and pch307 detects a small family of genes. These clones will provide the initial source of genes to manipulate and affect fruit development.

Free access

Abstract

Leaf chambers were placed on 6 leaves each of 3 trees of orange [Citrus sinensis (L.) Osbeck cv. Valencia] budded on rough lemon [Citrus limon (Lush) Burm. f.] rootstock, of which one tree was healthy and one in an early stage and one in an advanced stage of citrus blight, a decline disease of unknown etiology. Carbon dioxide exchange rates (CER) and leaf transpiration were measured every 7.5 minutes, continuously over a 2-week period. No difference in average leaf CER was observed among the 3 trees, but the decrease in leaf area associated with blight was confirmed. Leaf area index appeared not to have decreased sufficiently, even in the advanced-blight tree, to reduce light interception and thereby to reduce overall tree CER significantly.

Open Access

Melon plants grafted on Cucurbita rootstock may suffer from nutritional deficiencies due to reduced absorption and translocation of minerals to the foliage. Melon (Cucumis melo L.) cv. 6023 was grafted onto two interspecific Cucurbita rootstocks (Cucurbita maxima × Cucurbita moschata) ‘TZ-148’ and ‘Gad’. Nongrafted melons were used as controls. Two fertilization field experiments were conducted in walk-in tunnels in the northern Arava valley of southern Israel. Two fertigation regimes were used: 1) standard and 2) enriched for magnesium (Mg; 150 mg·L−1), manganese (Mn; 7.5 mg·L−1), and zinc (Zn; 0.75 mg·L−1) to increase the concentrations of the lacking elements. The enriched fertigation significantly increased Mn, Zn, and Mg contents in the leaf tissue. Concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), chloride (Cl), iron (Fe), and boron (B) were unaffected by the enriched fertilizer. There were no deficiency symptoms in grafted plants supplied with the enriched fertilizer.

Free access

We are interested in identifying and isolating genes which affect the rate of softening in peach fruit. It may be possible through the engineering of these genes to delay or extend the softening. This could ultimately allow for the harvest and transport of more mature, higher quality fruit. The clone, pch313, was isolated from a ripe peach fruit cDNA library. RNA homologous to this clone is detected at a low abundance in fruit until softening when a >100 fold increase in abundance of the RNA occurs. Pch313 RNA is also detected 30 min after wounding leaf or fruit tissue and peaks in accumulation within 2-8 hours. Wound ethylene was measured from the same tissue and its rate of evolution paralleled the accumulation of the RNA. The cDNA was sequenced and found to have 78% sequence identity with pTom13, a tomato gene that is expressed during fruit ripening and wounding (Holdsworth et al., NAR 15:731-739, 1987). To determine the universality of pch313 related gene expression, RNA accumulation was measured in other fruits during softening, and in leaf tissue upon wounding.

Free access

We are interested in identifying and isolating genes which affect the rate of softening in peach fruit. It may be possible through the engineering of these genes to delay or extend the softening. This could ultimately allow for the harvest and transport of more mature, higher quality fruit. The clone, pch313, was isolated from a ripe peach fruit cDNA library. RNA homologous to this clone is detected at a low abundance in fruit until softening when a >100 fold increase in abundance of the RNA occurs. Pch313 RNA is also detected 30 min after wounding leaf or fruit tissue and peaks in accumulation within 2-8 hours. Wound ethylene was measured from the same tissue and its rate of evolution paralleled the accumulation of the RNA. The cDNA was sequenced and found to have 78% sequence identity with pTom13, a tomato gene that is expressed during fruit ripening and wounding (Holdsworth et al., NAR 15:731-739, 1987). To determine the universality of pch313 related gene expression, RNA accumulation was measured in other fruits during softening, and in leaf tissue upon wounding.

Free access

The effect of Cucurbita and melon rootstocks on the horticultural and pathological performance of grafted Fusarium-susceptible melons was studied in four field experiments conducted in Fusarium-infested and Fusarium-free soils. The melon/melon combinations performed better than the melon/Cucurbita combinations regarding yield and disease control. In the 1999 experiment conducted in infested soil, Fusarium wilt symptoms were observed only in the nongrafted susceptible melons whereas all grafted combinations were symptom-free. In the 2000 experiment, nongrafted susceptible melons were totally wilted, whereas disease incidence in the melon/melon combinations and in one of the melon/Cucurbita combinations was low. The response of grafted plants to Fusarium wilt was also affected by the susceptibility of the scion. Among nongrafted melon cv. Ananas Ein Dor and those grafted onto Brava rootstock, 82% and 20%, were diseased, respectively, compared with only 36% and 0%, of the nongrafted and grafted `Ofir' melons, respectively. Negligible quantities of fruit were harvested from the nongrafted plants grown in infested soil, whereas high and moderate yields were obtained from melons grafted onto melon and Cucurbita rootstocks, respectively. The yield of the nongrafted melons in Fusarium-free soils were similar to those of all the grafted plant combinations. Susceptible melon scions grafted onto resistant melon rootstocks were less colonized by F. oxysporum f. sp. melonis than the same melons grafted onto the Cucurbita rootstocks.

Free access