Nematode-resistant Rootstocks Research Articles

Effect of some regulating substances on the vegetative parameters of flame seedless grapes cleft grafted on three nematode resistant rootstocks.

Grapes, the second next to Citrus, are one of Egypt's most popular fruits. Egypt is the world's 14th largest grape producers. The Flame seedless grape is a popular and early-season cultivar and one of the most prevalent grape kinds. Because the grape is nematode-sensitive, grafting on nematode-resistant rootstocks could be an effective way to minimize worm infection. The purpose of this study is to investigate the effect of IBA, Kinetin in graft union, and some grapevine rootstocks, such as Harmony, Freedom, and Salt Creek, on the percentage of Flame seedless grapevine survival and vegetative growth parameters when grafted using the cleft grafting method on the 15th February grafting date. When the Flame seedless grapes were treated at the graft union of the Freedom rootstock with a high level of indole-3-butyric acid (IBA, 1000 ppm) and a low level of Kinetin (250 ppm), they had a significantly higher survival percentage, shoot length, shoot diameter, L/D ratio, number of leaves per shoot, leaf area, fresh weight of leaves, fresh weight root system, dry weight of leaves and shoots, and dry weight root system in both seasons. It can be concluded that grafting on Freedom rootstock and using a low amount of Kinetin (250 ppm) are the most effective treatments for getting the highest percentage of survival and vegetative development parameters in Flame seedless grapevine.

Irrigation and Rootstocks to Manage Northern Root-Knot Nematode During Wine Grape Vineyard Establishment

Vineyard replanting in Washington state can be negatively impacted by the plant-parasitic nematode Meloidogyne hapla. Chemically focused nematode management programs do not offer long-term suppression; however, this may be achieved through the adoption of cultural approaches such as rootstocks and irrigation. Nematode-resistant rootstocks are used extensively in other regions but many have not been tested against M. hapla. Vineyards in eastern Washington are irrigated; therefore, manipulating available soil water may also impact nematode development. In 2017, two field trials were established in eastern Washington to evaluate the effects of (i) late-summer water limitation on M. hapla population development and (ii) host status of 1103 Paulsen, 3309 Couderc, and Matador rootstocks for M. hapla. The efficacy of these cultural management approaches was evaluated under three initial M. hapla densities (0, 50, and 250 M. hapla second-stage juveniles per 250 g of soil) in both trials. Reducing irrigation to manage M. hapla infestation of grape roots was ineffective and may cause harm to the vines by inducing too much water stress. Conversely, rootstocks effectively reduced population densities of M. hapla. Overall, rootstocks show the most promise as a cultural tool to manage M. hapla during the establishment phase in Washington vineyards.

Percent of Survival, Vegetative Growth and Hormonal Balance as Affected by Chip Budding of Flame Seedless cv. on Three Nematode Resistant Rootstocks

Percent of Survival, Vegetative Growth and Hormonal Balance as Affected by Chip Budding of Flame Seedless cv. on Three Nematode Resistant Rootstocks

Performance of ‘Chambourcin’ Winegrape on Nematode-resistant Rootstocks in Missouri

One of the most popular winegrapes (Vitis sp.) for red wine production in the midwestern United States is ‘Chambourcin’, a French-American hybrid. It is typically produced on own-rooted vines in the region, but the potential benefits of grafting it to improved rootstocks are becoming better-known. Nematodes present occasional serious winegrape production challenges in the midwestern United States, and are capable of transmitting pathogenic viruses. New rootstocks developed by University of California, Davis (UCD GRN series) are resistant to several species and races of nematodes, but have not been evaluated under midwestern U.S. production conditions. A study with ‘Chambourcin’ grafted to four of these new nematode-resistant rootstocks (‘UCD GRN-2’, ‘UCD GRN-3’, ‘UCD GRN-4’, and ‘UCD GRN-5’) and ‘Couderc 3309’, along with own-rooted vines was established in 2010 in southwest Missouri, and fruited in 2013–15. Three of the nematode-resistant rootstocks (GRN-2, 3, 4) performed as well as the standard ‘Couderc 3309’ and own-rooted vines, with yields among all rootstocks ranging from 10 to 13 kg/vine. The rootstock ‘UCD GRN-5’ generally performed poorly, however, manifested by low pruning weights and a high Ravaz index value (25) in 2013 that necessitated defruiting the vines in 2014. Fruit yields on ‘UCD GRN-5’ rootstocks were satisfactory in 2013 and 2015, but the vines eventually deteriorated, with 99% shootless nodes by 2017. Although more evaluations of these new rootstocks are needed in the midwestern United States, we conclude that ‘UCD GRN-2’, ‘UCD GRN-3’, and ‘UCD GRN-4’ show promise, whereas ‘UCD GRN-5’ does not appear suitable for growing conditions in southern Missouri.

Improved Resistance to Root-knot Nematode Species in an Advanced Inbred Line of Specialty Pepper (Capsicum annuum)

Bell and chili peppers are important vegetable and spice commodities worldwide. Significant yield reductions have been attributed to damage caused by root-knot nematodes (RKNs; Meloidogyne spp.). This study addresses the need for developing pepper varieties that have high resistance to RKN, which is now of increasing importance due to restrictions on the use of fumigant nematicides. Our goal is to provide a nonchemical alternative to sustain commercial pepper production in Florida, which is a major producer of peppers in the United States. We evaluated ‘UFRJ107(6)A3’, an advanced inbred line developed from a cross between Capsicum annuum L. ‘Jalapeno’ and ‘Round of Hungary’, for resistance against the nematode in comparison with the parental and three other Capsicum cultivars, namely, C. annuum ‘Charleston Belle’, ‘California Wonder’, and C. chinense Jacq. ‘Datil’ in two separate growth chamber experiments. Based on egg mass indices and reproduction factors, ‘UFRJ107(6)A3’ was significantly more resistant to M. incognita compared with the other five cultivars. When tested with five RKN species, ‘UFRJ107(6)A3’ showed comparably high levels of resistance to M. arenaria and M. floridensis as ‘California Wonder’ based on the nematode reproduction factor. In ‘UFRJ107(6)A3’, however, there were no detectable M. arenaria egg masses, and M. incognita reproduction was minimal compared with that of ‘California Wonder’; both cultivars supported the reproduction of M. enterolobii and M. javanica, although the reproduction factors of M. enterolobii were ≈10-fold higher than M. javanica. To characterize the mechanism of high resistance to M. incognita in ‘UFRJ107(6)A3’, we examined the extent to which infective second-stage juveniles (J2s) were able to penetrate its roots in comparison with the susceptible ‘California Wonder’ and ‘Datil’ in two independent experiments; we conducted RKN root penetration assays with a single plant in a pot and two plants in a single-pot choice test using ‘Datil’ and ‘California Wonder’, respectively, as susceptible standards. In both assays, M. incognita J2s were absent in the roots of ‘UFRJ107(6)A3’ 7 days after inoculation but were present in the susceptible cultivars, indicating that resistance has an effect at the root invasion stage. In growth chamber experiments, at constant temperatures of 28 and 30 °C, ‘UFRJ107(6)A3’ exhibited M. incognita resistance superior to its parents and to the standard resistant bell pepper ‘Charleston Belle’, thus offering the potential to enhance specialty pepper production and for use as a nematode-resistant rootstock for commercial bell peppers.

Rootstocks Improve Blanc Du Bois Vine Performance and Fruit Quality on Alkaline Soil

Summary Goals: Blanc Du Bois is the most widely planted Pierce’s Disease (PD) tolerant white wine grape variety in Texas. However, on alkaline soils, which are widespread across the state, nutritional deficiencies have been observed in own-rooted vines. This work evaluated the impact of rootstock on Blanc Du Bois vine growth, nutritional status, and fruit composition on an alkaline vineyard site in the Texas Gulf Coast. Ten rootstocks representing common rootstocks in Texas (Paulsen 1103, Kober 5BB, Teleki 5C), nematode resistant rootstocks (UCD-GRN1, UCD-GRN2, UCD-GRN3, UCD-GRN4 and UCD-GRN5), and rootstocks with believed tolerance to cotton root rot (Phymatotricopsis omnivorum) (Ramsey, Dog Ridge) were studied over a four-year period. Key Findings: UCD-GRN1 rootstock performed poorly as a result of severe magnesium and iron deficiency. Ramsey maintained the most favorable nutritional status and consistently produced the highest pruning weights. Own-rooted Blanc Du Bois had lower fruit quality when compared to most rootstocks (Ramsey, Dog Ridge, UCD-GRN2, UCD-GRN3, UCD-GRN4, UCD-GRN5, Paulsen 1103, Kober 5BB), although vine size (pruning weight) and crop load (yield:pruning weight) were generally comparable. In 2015 and 2016, juice pH positively correlated with juice potassium with concentrations of potassium varying by an average of approximately 20% across rootstocks. On average, own-rooted Blanc Du Bois tissue samples contained 323% more sodium than grafted vines. Impact and Significance: This study demonstrated that Blanc Du Bois can benefit from grafting onto rootstocks on alkaline soils. Own-rooted Blanc Du Bois vines were generally less productive than Paulsen 1103, Dog Ridge, UCD-GRN3, and Ramsey likely as result of nutritional status. Own-rooted Blanc Du Bois also had lower soluble solids at harvest than most rootstocks as a result of diminished nutritional status, although titratable acidity and pH were not consistently different. Delaying harvest did not result in a further increase in soluble solids, although acidity continued to decrease, suggesting that own-rooted Blanc Du Bois was not simply behind in physiological maturity, but rather produced lower quality fruit than most of the rootstocks under study. The poor performance of UCD-GRN1 throughout the study suggests that it is not adapted to alkaline soils.

Evaluation of Grapevine Rootstocks on Slightly Acidic and Strongly Alkaline Texas Hill Country Soils

Summary Goals: Rootstock selection is usually dictated by vineyard site conditions such as pest and disease pressure, soil, and climate. This work evaluated the impact of rootstock on ‘Sangiovese’ vine size, nutritional status, and fruit composition at two sites in the Texas Hill Country, one with a slightly acidic (pH 6.58 ± 0.05) loamy fine sand soil and the other with a moderately to strongly alkaline (pH 8.48 ± 0.06) clay loam soil. Eleven rootstocks representing common rootstocks in Texas (‘Paulsen 1103’, ‘Kober 5BB’, ‘Teleki 5C’), nematode resistant rootstocks (‘UCD GRN-1’, ‘UCD GRN-2’, ‘UCD GRN-3’, ‘UCD GRN-4’ and ‘UCD GRN-5’), and rootstocks with possible tolerance to cotton root rot (Phymatotricopsis omnivora) (Ramsey, Dog Ridge, Florilush) were studied over a five-year period. Key Findings: At the Real County test site, in an alkaline clay loam soil, the rootstocks ‘Dog Ridge’ and ‘Teleki 5C’ maintained the most favorable nutrient status resulting in higher vine vigor and dormant cane pruning weights with pruning weights averaging 0.52 kg/vine and 0.37 kg/vine, respectively, versus 0.09 kg/vine for own-rooted ‘Sangiovese’. The rootstocks ‘Florilush’, ‘UCD GRN-1’, ‘UCD GRN-5’, and own-rooted ‘Sangiovese’ performed poorly at the Real County test site as a result of nutritional deficiency. At the Gillespie County site, in a slightly acidic loamy fine sand soil, all rootstocks performed acceptably with respect to vine size, nutrition, and fruit composition, although average dormant pruning weights over five years ranged across rootstocks from 0.52 to 0.87 kg/vine. Petiole potassium and magnesium were inversely correlated across rootstocks, with the strongest relationship (R2 = 0.58) observed in late summer at the Gillespie County site. Own-rooted ‘Sangiovese’ maintained the lowest petiole potassium and highest petiole magnesium concentrations over the study, as well as the lowest juice potassium and pH at the Gillespie County site. Juice potassium and pH were positively correlated (R2 = 0.57 and 0.76) across rootstocks in two out of three years of study at the Gillespie County site. Impact and Significance: This study demonstrated the importance of rootstock selection on a moderately to strongly alkaline soil versus a slightly acidic soil. Out of the eleven rootstocks tested, only ‘Dog Ridge’ and ‘Teleki 5C’ produced an acceptably sized (0.25 and 0.16 kg/m canopy) mature vine (fourth leaf) likely as a result of nutrition. All rootstocks under study resulted in petiole iron concentrations below recommended values, but the severity of shoot tip chlorosis, which is associated with iron deficiency, was highly rootstock dependent. The rootstocks with the lowest pruning weights and vigor ratings at the Real County site (own-rooted ‘Sangiovese’, ‘Florilush’, ‘UCD GRN-1’, and ‘UCD GRN-5’) generally expressed the most shoot tip chlorosis. Addressing this apparent nutritional deficiency with targeted fertilizer applications may have improved vine performance, but this research suggests that proper rootstock selection is a more viable option. The impact of rootstock was less apparent on slightly acidic loamy fine sand soil. All rootstocks and own-rooted ‘Sangiovese’, conferred acceptable pruning weights, nutritional status, and fruit composition. Basic juice chemistry did vary by rootstock while own-rooted ‘Sangiovese’ having the lowest juice potassium and pH, but the risks of growing own-rooted V. vinifera likely outweigh this potential benefit on sites where climate, soil conditions, pests, or disease may be limiting.

Effect of grafting date and rootstock type on vegetative growth parameters of Flame seedless grape grafted on three nematode resistant rootstocks

Effect of grafting date and rootstock type on vegetative growth parameters of Flame seedless grape grafted on three nematode resistant rootstocks

Rootstocks for Florida Stone Fruit

Rootstocks have been used in many tree fruit systems to provide growth advantages and/or pest and disease resistance without affecting (or sometimes improving) productivity and fruit quality. In Florida, stone fruit are grown on rootstocks that specifically provide resistance to the peach root-knot nematode, Meloidogyne floridensis (Handoo, et al., 2004; Sherman, et al., 1991). Although several root-knot nematode-resistant rootstocks are available for stone fruit grown in other locations and climates, ‘Flordaguard’ peach rootstock is currently the only rootstock recommended for stone fruit production in Florida.
 
 Root-knot nematodes (M. incognita and M. javanica) have historically been the most important species of root-knot nematodes parasitizing peach in the southeastern United States peach industry. ‘Guardian’, ‘Nemaguard’, ‘Nemared’, and ‘Okinawa’ rootstocks are resistant to these species of nematode. However, in 1966 a new species of root-knot nematode was detected on ‘Nemaguard’ and ‘Okinawa’ peach rootstocks in Gainesville, Florida, and ultimately identified as M. floridensis in 2004 (Han-doo, et al., 2004). This nematode reproduces abundantly on ‘Nemaguard’ and ‘Nemared’ peach rootstocks as well as on other crops (verbena, eggplant, squash, basil, impatiens, tomato, snapdragon, dill, and certain ornamental plants) (Table 1). Consequently, ‘Nemaguard’, ‘Nemared’, and ‘Okinawa’ peach rootstock are no longer recommended for peaches, nectarines, and plums in Florida. ‘Nemaguard’ and ‘Nemared’ rootstocks had been used in north Florida for many years, but continued use may increase nematode populations to damaging levels on these rootstocks.
 
 ‘Flordaguard’ rootstock has better resistance to M. floridensis than ‘Nemaguard’ rootstock. Field evaluation of peach rootstocks to different root-knot nematode species indicated that after 25 months, nematode egg production was greater on ‘Nemaguard’ than on ‘Flordaguard’ rootstock (Nyczepir, et al., 2006). Longer-term observations in Florida also suggest that trees on ‘Nemaguard’ rootstock do not perform well in soils infested with M. floridensis. Accordingly, ‘Flordaguard’ rootstock is the only rootstock the University of Florida currently recommends for commercial peach production. ‘Sharpe’, a clonal plum hybrid rootstock (Beckman, et al., 2008), is only recommended for backyard fruit production because of its reduced yield and smaller fruit size when compared to trees budded onto ‘Flordaguard’ rootstock.

SNP markers tightly linked to root knot nematode resistance in grapevine (Vitis cinerea) identified by a genotyping-by-sequencing approach followed by Sequenom MassARRAY validation.

Plant parasitic nematodes, including root knot nematode Meloidogyne species, cause extensive damage to agriculture and horticultural crops. As Vitis vinifera cultivars are susceptible to root knot nematode parasitism, rootstocks resistant to these soil pests provide a sustainable approach to maintain grapevine production. Currently, most of the commercially available root knot nematode resistant rootstocks are highly vigorous and take up excess potassium, which reduces wine quality. As a result, there is a pressing need to breed new root knot nematode resistant rootstocks, which have no impact on wine quality. To develop molecular markers that predict root knot nematode resistance for marker assisted breeding, a genetic approach was employed to identify a root knot nematode resistance locus in grapevine. To this end, a Meloidogyne javanica resistant Vitis cinerea accession was crossed to a susceptible Vitis vinifera cultivar Riesling and results from screening the F1 individuals support a model that root knot nematode resistance, is conferred by a single dominant allele, referred as MELOIDOGYNE JAVANICA RESISTANCE1 (MJR1). Further, MJR1 resistance appears to be mediated by a hypersensitive response that occurs in the root apical meristem. Single nucleotide polymorphisms (SNPs) were identified using genotyping-by-sequencing and results from association and genetic mapping identified the MJR1 locus, which is located on chromosome 18 in the Vitis cinerea accession. Validation of the SNPs linked to the MJR1 locus using a Sequenom MassARRAY platform found that only 50% could be validated. The validated SNPs that flank and co-segregate with the MJR1 locus can be used for marker-assisted selection for Meloidogyne javanica resistance in grapevine.

Potential existence of multiple Tylenchulus semipenetrans biotypes in South Africa

The existence of multiple Tylenchulus semipenetrans biotypes within a citrus-producing region complicates the selection of nematode-resistant rootstocks for managing the slow decline of citrus. The potential existence of multiple T. semipenetrans biotypes in South Africa was investigated under greenhouse conditions on differential host plants using nematode isolates from 18 citrus-producing districts with at least six diverse soil groups and three different climates. After three nematode generations, the regional effects had no influence on final nematode population densities, whereas the differential host plants significantly segregated the nematode reproductive potentials. On Olea europaea reproductive potentials (eggs and juveniles/g) were zero, whereas those on Citrus jambhiri and Poncirus trifoliata ranged from 79 to 482 and 86 to 433, respectively. All T. semipenetrans isolates, regardless of the soil group and climate type, behaved similarly to the Poncirus biotype, which therefore rules out the existence of multiple T. semipenetrans biotypes in South Africa.

HYBRID AND SELFED SEEDLING PROGENIES OF VITIS HYBRID 'ROGER'S RED' GRAPE SEGREGATE FOR TENDRIL DISTRIBUTION

Grapevines of most species and cultivars produce lateral meristems (tendrils and inflorescences) on at least two successive nodes in three. Lateral meristems complicate rootstock cutting production, since tendrils are removed from rootstock cuttings prior to propagation and since tendrils clinging to wires, canes, or other tendrils make collecting cuttings more time consuming and expensive. To develop improved grapevine rootstocks with reduced lateral meristems, an elite nematode resistant rootstock selection ((Vitis berlandieri × V. riparia) × V. biformis) was crossed with ?Roger?s Red? (Vitis hybrid), and ?Roger?s Red? was also self-pollinated. Seedlings from controlled pollinations were grown in a greenhouse and trained up a stake. Starting at the first node in alternate phyllotaxy (that is, a node with a lateral meristem) and continuing for twelve nodes, the presence or absence of lateral meristems was observed and the type of lateral meristem was reported. There were 141 cross-pollinated seedlings. There were 83 seedlings from ?Roger?s Red? self-pollination. The expected pattern of lateral meristem distribution was wild type: two successive lateral meristem bearing nodes, followed by a single lateral meristem-free node. However, 43 of 83 seedlings from ?Roger?s Red? self-pollination showed two or more successive lateral meristem-free nodes (flanked by lateral meristem-bearing nodes), and 12 of these 43 showed at least two sets of two successive lateral meristem-free nodes. One self-pollinated seedling showed three successive lateral meristem-free nodes in the alternate phyllotaxy. In contrast, in the hybrid population only 33 of 141 seedlings showed the non-wild type pattern of two successive lateral meristem-free nodes, and only 6 of these 33 showed at least two sets of two successive lateral meristem-free nodes. Tendril distribution is under genetic control and the production of extra tendril-free nodes was segregating in these populations. Dominant alleles at two genes are required for the mutant phenotype. A genetic model and the gene names Successive Tendril free Node-1 and Successive Tendril free Node-2 are proposed.

New pepper accessions proved to be suitable as a genetic resource for use in breeding nematode-resistant rootstocks

Root-knot nematodes (RKNs), Meloidogyne spp., are considered, worldwide, as one of the main pathogens of solanaceous crops, including pepper (Capsicum spp.). Restrictions on the use of standard nematicides have motivated the development and use of resistant cultivars and rootstocks. Three genes in pepper, called Me1, Me3 and N, confer resistance to the three main RKN species (Meloidogyne incognita, Meloidogyne javanica and Meloidogyne arenaria). However, their effectiveness seems to be limited because nematode populations that have overcome the resistance have been found, leading to a search for new sources of resistance and strategies to preserve their effectiveness. In two greenhouses and over a 7-month growing period, we evaluated the resistance to M. incognita and the agronomic behaviour as rootstocks of nine pepper (Capsicum annuum) accessions – HDA330 (Me1 carrier), Serrano Criollo de Morelos, (Me3 carrier), Yolo Wonder (partially resistant) and another six accessions of unknown resistance originating from cultivars well adapted to the local growing conditions. The resistance conferred by the Me1 gene was more robust than that conferred by Me3. Resistance to M. incognita was found in four new accessions: P13, CTL, CT5, and P14. In P13, the level of resistance was similar to that of HDA330. The resistant accessions showed better agronomic behaviour than the susceptible accessions, which was most noticeable towards the final of the growing period. Some accessions constitute a potential resource for use in the genetic breeding of RKN-resistant rootstocks.

Accessions of Citrullus lanatus var. citroides Are Valuable Rootstocks for Grafted Watermelon in Fields Infested with Root-knot Nematodes

Root-knot nematode-resistant rootstock lines (designated RKVL for Root-Knot Vegetable Laboratory) derived from wild watermelon (Citrullus lanatus var. citroides) were compared with wild tinda (Praecitrullus fistulosus) lines and commercial cucurbit rootstock cultivars for grafting of seedless triploid watermelon ‘Tri-X 313’ (C. lanatus var. lanatus) in a field infested with the southern root-knot nematode (RKN) (Meloidogyne incognita) in Charleston, SC, during 2009 and 2010. In both years, RKN infection was severe in ‘Emphasis’ bottle gourd, ‘Strong Tosa’ hybrid squash, and wild tinda rootstocks with galling of the root system ranging from 86% to 100%. In 2009, the RKVL wild watermelon rootstocks exhibited lower (P < 0.05) percentages of root galling (range 9% to 16%) than non-grafted ‘Tri-X 313’ (41%), ‘Emphasis’, ‘Strong Tosa’, and the wild tinda rootstocks. The grafted wild watermelon rootstock RKVL 318 produced more (P ≤ 0.05) fruit (12 per plot) than all other entries (mean = five per plot), and it produced a heavier (P ≤ 0.05) fruit yield (29.5 kg per plot) than all entries except self-grafted ‘Tri-X 313’ (21.5 kg per plot). In 2010, soil in half of the plots was treated with methyl bromide (50%):chloropicrin (50%) (392 kg·ha–1) before planting. The RKVL wild watermelon rootstocks exhibited resistance to RKN with percentages of root system galled ranging from 11% for RKVL 316 to 56% for RKVL 301 in the untreated control plots. Fruit yields in the untreated plots were 21.9, 25.6, and 19.9 kg/plot for RKVL 301, RKVL 316, and RKVL 318, respectively. Yields were greater (P ≤ 0.05) for the three RKVL rootstocks than for ‘Strong Tosa’ (3.0 kg) and ‘Ojakkyo’ wild watermelon rootstock (2.8 kg) in the untreated plots. Yields of watermelon grafted on ‘Strong Tosa’ were nearly seven times greater (P ≤ 0.05) in the methyl bromide-treated plots than in the untreated plots. In contrast, yields of RKVL 316 and RKVL 318 were similar in both treatments and the yield of RKVL 301 was less (P ≤ 0.05) in the methyl bromide-treated plots than in the untreated plots. The three RKVL wild watermelon rootstock lines exhibited resistance to RKN. RKVL 316 had low root galling and produced the heaviest fruit yield and greatest numbers of fruit of any rootstock evaluated in 2010. The RKVL lines should be useful sources of RKN resistance for rootstocks for grafted watermelon.

A new grafted rootstock against root-knot nematode for cucumber, melon, and watermelon

Southern root-knot nematode causes dramatic galling on the roots of cucurbitaceous plants such as cucumber, melon, and watermelon. Even low nematode levels can cause high yield losses. Control of root-knot nematode is usually based on soil fumigation with toxic methyl bromide. However, since methyl bromide is now banned, growers are looking for alternative pest control. A potential solution is to graft susceptible scions onto nematode-resistant rootstocks. Here, we selected a Meloidogyne incognita-resistant rootstock suitable for cucumber, melon, and watermelon scions. First, we screened the resistance against nematode and Fusarium. Then, we tested a wild Cucumis species, Cucumis pustulatus, as a possible rootstock for cucumber, melon, and watermelon scions. We measured the survival rate, plant growth, yield, and fruit quality of grafted plants. Fifty-three accessions from 16 species were studied. Five accessions exhibited high resistance to southern root-knot nematode, and 12 accessions exhibited resistance to Fusarium wilt. This research is the first study to report that C. pustulatus is a suitable rootstock with simultaneous resistance to root-knot nematode and Fusarium wilt for cucumber, melon, and watermelon. C. pustulatus rootstocks are thus promising for low-input sustainable horticulture. They should benefit to home gardeners, especially to those in areas highly infested with southern root-knot nematode.

Rootstocks for Florida Stone Fruit

Rootstocks have been used in many tree fruit systems to provide growth advantages or pest or disease resistance without affecting productivity and fruit quality. In Florida, stone fruit are grown on rootstocks that specifically provide pest resistance to the peach root-knot nematode. Although several root-knot nematode-resistant rootstocks are available for stone fruit grown in other locations and climates, ‘Flordaguard’ peach rootstock is currently recommended for stone fruit production in Florida. This revised 5-page fact sheet was written by M. Olmstead, J. Chaparro, and J. Ferguson, and published by the UF Department of Horticultural Sciences, November 2012. HS1110/HS366: Rootstocks for Florida Stone Fruit (ufl.edu)

Host-status and host-sensitivity of wild Cucumis species to Meloidogyne incognita race 4

Wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus), which are highly resistant to the southern root-knot nematode (Meloidogyne incognita) race 2, have the potential for serving as seedling rootstocks for the highly nematode-susceptible watermelon (Citrullus lanatus) cultivars. In South Africa, due to high labour costs, most cotton farmers are turning to watermelon production. In these regions, there is high incidence of M. incognita race 4. A pot experiment in the greenhouse was, therefore, initiated to investigate the host-status and host-sensitivity of Cucumis africanus and Cucumis myriocarpus to M. incognita race 4, when inoculated with 0, 200, 600, 100, 1400, 1800 and 2200 eggs and second-stage juveniles (J2s). At harvest, 56 days after inoculation, the reproductive factor values at all levels of inoculation were less than one. Penetration indices on both plant species were greater than one, suggesting that the resistance was post-infectional and therefore, introgressible. Sex (male: female) ratios of M. incognita race 4 on the two Cucumis species were greater than one, suggesting that more J2s were converted into males. Infection of Cucumis species by the test nematode had no effect on yield components of the two plant species due to poor feeding sites. The two Cucumis species were, therefore, resistant to M. incognita race 4, with post-infectional resistance, where the sex ratio was skewed towards maleness. Thus, the two Cucumis species have the potential to be used as nematode-resistant rootstocks in watermelon production.

Host Suitability ofVitisandVitis-MuscadiniaMaterial to the NematodeXiphinema indexover One to Four Years

The dagger nematode <i>Xiphinema index</i> specifically transmits <i>Grapevine fanleaf virus</i> (GFLV), which causes progressive grape degeneration in vineyards worldwide. Nematode-resistant rootstocks are a promising alternative to the ban of nematicides. We report the evaluation, under controlled conditions in two independent experiments, of the host suitability (reproduction factor, RF) of 40 <i>Vitis</i> and <i>Vitis</i>-<i>Muscadinia</i> accessions to the isofemale line Fréjus of <i>X. index.</i> In the first experiment, 17 accessions, grown from either in vitro culture or cuttings, were evaluated after 1 and 3 years and, for four accessions, also after 4 years. The nematode multiplied early and late on reference rootstocks <i>V. rupestris</i> du Lot and <i>V. riparia</i> Gloire de Montpellier, respectively. Among <i>Vitis</i>-<i>Muscadinia</i> material, after 1 and 3 years, accession VRH 8624 had high RFs, while VRH 8771 and NC 35–50 had RFs close to 1. The nematode-resistant candidate rootstock accession RPG1 (=VRH 8771 x <i>Vitis</i> rootstock 140Ru) and the intergeneric hybrid VRH 97-99-79 had RFs significantly higher at 4 years than at 1 year, suggesting a progressive adaptation of the nematode to the plant resistance factors. Most <i>Vitis</i> botanic accessions had high RFs at both 1-year and 3-year durations. Low RFs, observed for the remaining accessions, were probably due to the poor root development and the subsequent difficult access of nematodes to feeding on this material. In the second experiment, 23 <i>Vitis</i> accessions, evaluated only at 3 years, had high RFs, except for a few accessions that expressed low RFs and poor development. Thus some muscadine-derived intergeneric hybrids are promising resistance sources that must be confirmed using nematode lines from other geographic origins.

Plant-parasitic nematodes in Australian viticulture: key pests, current management practices and opportunities for future improvements

This paper provides a brief overview of the Australian grape industry and discusses the distribution and economic importance of its main nematode pests and outlines the management practices (hot water treatment of planting material, nematode-resistant rootstocks and nematicides) that are currently used to minimise losses from nematodes. However, the main focus of the paper is the research that will be required to improve current practices for managing nematodes. Topics covered include: (i) methods of producing nematode-free planting material; (ii) breeding programs to develop rootstock material suitable for local conditions; (iii) the use of molecular-assisted selection and genetic modification to develop transgenic grapevines and rootstocks with resistance to several nematode species; (iv) options for enhancing naturally occurring biological controls; (v) the introduction of agronomic practices that improve the capacity of grapevines to withstand attack from nematodes; and (vi) the development of farming systems that improve soil physical, chemical and biological properties and enhance the suppressiveness of soil to nematodes.

Advanced generation peach-almond hybrids as seedling rootstocks for almond: first year growth and potential pollenizers for hybrid seed production

For decades, seedling peaches have been used as the standard rootstock in California almond orchards. Vigorous, deep rooted trees are needed in almond orchards for maximum yields and to withstand the annual tree-shaking at harvest. Currently, researchers are actively evaluating rootstocks for almonds in field trials and in various screening protocols. In this study, seedling rootstocks, obtained from male-sterile advanced generation peach-almond (PEAL) hybrid mother trees, were compared with ‘Nemaguard’ peach seedlings for emergence in the nursery row, trunk caliper at propagation time, and end of season dormant above ground tree weight. Seedling emergence was affected significantly (P ≤ 0.05) by seed source, as was trunk caliper and end of season dormant above ground tree weight. Trunk caliper and dormant above ground tree weight were also affected significantly (P ≤ 0.05) by planting year. Results obtained in this study demonstrate the enhanced first year growth from seedlings of advanced generation PEAL hybrids, as compared to ‘Nemaguard’ seedlings. Seedling emergence in the rootstock bed was not affected significantly by planting year. Advanced generation PEAL hybrid seedlings were ready for June-budding at an earlier date compared to ‘Nemaguard’ seedlings, providing the potential for larger-sized finished nursery stock by the end of the growing season. Due to the male-sterile status of the advanced generation PEAL mother trees, bloom periods of several root-knot nematode resistant rootstock cultivars were examined for their degree of synchronicity with the mother trees. The examined rootstocks and mother trees varied in both chill hour and post-chill heat requirements necessary to effect bloom. ‘Flordaguard’ peach rootstock began bloom in advance of the male-sterile mother trees, whereas the bloom period of ‘Tsukuba No. 4’ occurred well after, suggesting they would not be effective synchronous pollenizers for consistent hybrid seed production. Based on more limited flowering period data, better bloom synchronicity was achieved with a Tsukuba No. 4 X Flordaguard hybrid.