Rootstock Resistance Research Articles

Effect of Spirulina platensis extract on growth potential of in vitro culture pear

Pears are among the most economically important fruits in the world that are grown in all temperate zones. ‘Le-Cont’ rootstock pear is one of the gene sources used to improve fruit productivity, rootstock resistance, and tolerance to biotic and abiotic stresses. Traditional propagation of pear. Pear is time-consuming and limited by a short growing season and hard winter conditions. Therefore, in vitro propagation is a suitable alternative method. Murashige and Skoog medium (MS) and spirulina platensis extract at 5,10 and 20 % supplemented with different concentrations (0.25, 0.5 and 1.0 mg/l) of 6-benzyladenine (BA) and kinetin (Kin), individually or in combination with them. Treatments were used for in vitro shoot proliferation. Nodal segments were used as explants. MS medium augmented was 3mg/l 6-benzyladenine (BA) plus 20 % Spirulina platensis extraction then used for shootlets proliferation of micro-shoots. A combination of 3 mg/l BA and 20 % Spirulina platensis as a growth media resulted in a significant improvement in shoot proliferation. This combination produced the highest number of shoots (2.8 per explant) and leaves (6.3 per explant) similar with those containing MS media plus 20% extraction (2.9 per explant) and leaves (6.8 per explant). The longest shoots (2.97 cm) were obtained in each previous treatment. However, these shoots were similar with those produced from classical multiplication by MS according to ISSR analysis which scored 89.1 % of mono morphism percentage and 10.1 % polymorphism. The ISSR analysis shows the highest similarity index percentage for P5-P9 0.986301.

Effects of two apple rootstocks on the soil microecology of replanted apple orchard soil

Apple replant disease (ARD) seriously restricts the development of the apple industry. It is of great significance for the sustainable development of the apple industry to alleviate ARD by using rootstock resistance. Taking M9T337 and Malus robusta Rehd. as test materials, the differences in biomass, soil physical and chemical properties, soil enzyme activity, soil microbial metabolic activity and carbon source utilization characteristics, soil microbial quantity, and soil fungal community of two apple rootstocks in replanted soil. The results showed that the biomass, related soil enzyme activities, and AWCD metabolic activity of apple saplings with Malus robusta Rehd. as rootstock were better, the number of soil fungi and the copy number of four Fusarium genes were lower, and more beneficial bacteria were enriched. In conclusion, the apple saplings with Malus robusta Rehd. as rootstock have a better improvement effect on the replanted soil environment and are more suitable as rootstocks to prevent and control ARD than M9T337.

Rootstock resistance to apple replant disease

Rootstock resistance to apple replant disease

Resistance of the citrus rootstock forner-alcaide 5 to Tylenchulus semipenetrans in replant situations

The resistance of the citrus rootstock Forner-Alcaide 5 to Tylenchulus semipenetrans was assessed in comparison to the susceptible Carrizo citrange (S) in two replant situations. Changes in soil and root population densities were monitored after planting the new trees to detect tree infection and nematode population growth over time. The efficacy of pre-plant control methods such as fumigation with 1,3 Dichloropropene (1,3D) or 2-year fallowing was also assessed. Fumigation and fallowing reduced juveniles + males/250 cm3 soil to undetectable levels for 3 and 2 years, respectively, and postponed root parasitism on Forner-Alcaide 5 for 3 and 2.5 years, respectively. Forner-Alcaide 5 supported lower densities of juveniles + males/250 cm3 soil and females/g root than Carrizo citrange in both replant situations The efficacy of the resistant rootstock was enhanced when combined with 1,3D fumigation or 2-year fallowing because the pre-planting control reduced densities of juveniles + males in soil before establishing the orchard, and the resistant rootstock, the female densities in the roots. Selection for virulence within the field population did not occurr after 9-years of exposure of Forner-Alcaide 5 to the nematode. The durability of the resistance can be enhanced by combining rootstock resistance with pre-planting control methods in order to delay root parasitism, and therefore, diminish the selection pressure exerted on the resistant rootstock. Forner-Alcaide 5 exibited higher scion diameter and yield than Carrizo citrange.

Optimization of In Vitro Propagation of Pear (Pyrus communis L.) ‘Pyrodwarf®(S)’ Rootstock

Pears are among the most economically important fruits in the world that are grown in all temperate zones. Pyrus communis L., ‘Pyrodwarf®(S)’ rootstock is one of the gene sources used to improve fruit productivity, rootstock resistance, and tolerance to biotic and abiotic stresses. Traditional propagation of P. communis L. is time-consuming and limited by a short growing season and harsh winter conditions. Therefore, in vitro propagation is a suitable alternative. Murashige and Skoog medium (MS) and woody plant medium (WPM) supplemented with different concentrations of 6-benzyladenine (BA) and kinetin (Kin), individually or in combination, were used for in vitro shoot proliferation. Nodal segments were used as explants. MS medium augmented with indole-3-butyric acid (IBA) or indole-3-acetic acid (IAA) was then used for rooting of microshoots. A combination of 2 mg·L−1 BA and 1 mg·L−1 Kin in MS medium resulted in a significant improvement in shoot proliferation. This combination produced the highest number of shoots (4.352 per explant) and leaves (10.02 per explant). The longest shoots (4.045 cm) were obtained in WPM enriched with 1 mg·L−1 BA. However, these shoots were not suitable for multiplication and rooting steps. The largest number of roots (5.50 per microshoot) was obtained on MS medium augmented with IAA at 1 mg·L−1. The produced plantlets were cultivated in pots filled with perlite and cocopeat (in a ratio of 1:3) and acclimatized gradually in a greenhouse, recording an even 90% survival rate.

Effect of Gene Silencing of Translation Initiation Factors eIF(iso)4G and eIF(iso)4E on Sour Cherry Rootstock Resistance to Sharka Disease.

Sharka disease, caused by the Plum pox virus (PPV), is one of the most harmful, quarantine viral diseases that affect stone fruit crops. The absence of natural resistance to the virus in stone fruits has become a decisive factor for the use of genetic transformation methods to obtain stable forms. The eIF(iso)4G and eIF(iso)4E genes encode translation initiation factors used in the PPV life cycle. In the presented study, the effect of silencing these genes using the RNA interference method on the resistance of sour cherry rootstock 146-2 plants (Prunus pumila L. x Prunus tomentosa Thunb) to the sharka disease was studied. Two vectors have been created for the genetic transformation of plants, with self-complementary sequences of the eIF(iso)4G and eIF(iso)4E gene fragments. The hairpin expression cassette contains a strong promoter of the peach ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) gene, as well as an intron and terminator of the same gene. We used the pMF1 vector containing recombinase R and a codA-nptII gene which makes it possible to obtain intragenic marker-free plants. A successful genetic transformation was carried out by the AGL0 strain of A. tumefaciens. Whole leaves of shoots cultivated in vitro were used as a source of explants. Eight independent transgenic lines of rootstock 146-2 were obtained in experiments (sixlines with a hairpin to the eIF(iso)4G gene and two lines with a hairpin to the eIF(iso)4E gene). Their status was confirmed by the PCR and Southern blotting. The obtained plants were acclimatized in a greenhouse. The silencing of the eIF(iso)4G and eIF(iso)4E genes in transgenic plants was confirmed by the quantitative PCR. The presence of specific small interfering (si) RNAs was confirmed by the method of Northern blotting. Plants of all transgenic rootstock lines were infected with PPV by the method of grafting with infected buds. Resistance to the PPV infection of the obtained transgenic plants was carried out by using an enzyme immunoassay. The ELISA results showed that silencing the eIF(iso)4G gene did not lead to increased resistance while silencing the eIF(iso)4E factor gene led to increased resistance to the PPV, and the one line's plants showed no signs of infection for two years after infecting. The work demonstrates a (promising) approach in which the creation of stone cultures resistant to the plum pox virus can be achieved by suppressing the genes of translation initiation factors in clonal rootstocks.

Evaluation of Apple Chlorotic Leaf Spot Virus Impact on Fruit Yield and Vegetative Growth in Apple Cultivars ‘Antonovka’ and ‘Gita’

Abstract The negative influence of pathogens on plant development is well known. However, the negative impact depends on various factors: cultivar and rootstock resistance, nutrition, the environment, the virulence, and concentration of pathogens in the plant tissue. The evaluation of apple chlorotic leaf spot virus (ACLSV) influence on apple tree growth and production was performed at Institute of Horticulture (LatHort) from 2012 to 2020. Virus-free and ACLSV-infected trees from the traditional cultivar ‘Antonovka’ and new scab resistant cultivar ‘Gita’ were evaluated on dwarfing rootstock B.396. The presence of four common apple viruses (apple mosaic virus (ApMV), ACLSV, apple stem grooving virus (ASGV), apple stem pitting virus (ASPV)) was assayed in the planting year and repeated at the end of the study period. The vigour of planting material, growth, yield, and yield efficiency were compared between virus negative and ACLSV-infected trees. During eight growing seasons (2013–2020), no statistically significant negative impact of ACLSV infection on tree growth or yield was observed for the cultivars. A larger canopy volume was observed for ACLSV-infected trees (p = 0.01), but the cumulative yield per canopy volume was equivalent between virus-negative trees and ACLSV-infected trees (p = 0.07).

Screening Potential Citrus Rootstocks for Phytophthora nicotianae Tolerance

Seeds from four citrus rootstocks including sour orange, Bitters-C22 citrandarin, Sarawak pummelo Rio Red grapefruit, and Sarawak pummelo Bower mandarin were exposed to high inoculum levels of Phytophthora nicotianae to screen for tolerance. Inoculation of pregerminated seeds (PGIS) and non-PGIS was carried out. The average P. nicotianae propagule counts from the soil samples where these seedlings were raised ranged from 424 to 1361 colony forming units/cm3. The proportion of live to dead plants was recorded at 11 months postinoculation, which showed that Sarawak Bower performed significantly better than other rootstocks. Evaluation of the rootstocks 18 months postinoculation resulted in only one surviving sour orange plant, which suggests potential rootstock resistance.

Reaction of wild eggplant Solanum torvum to different species of root-knot nematodes from Turkey

The cultivated eggplant species are susceptible to root-knot nematodes (Meloidogyne spp.). However, many wild Solanum species, such as S. torvum, S. sisymbriifolium, S. aethiopicum and S. warscewiczii, are resistant to some root-knot nematodes. Only S. torvum is employed as a rootstock for eggplant cultivation worldwide. This study investigated the response of S. torvum cv. Hawk against the root-knot nematodes Meloidogyne incognita, Mi-1 virulent M. incognita, M. javanica, M. arenaria and M. luci and M. hapla from Turkey, under controlled conditions. A local eggplant cultivar and a commercial eggplant hybrid were included in the bioassay. Eggplant seedlings were each inoculated with 1000 second-stage juveniles of Meloidogyne spp. and uprooted 8 weeks after nematode inoculation. Then, egg masses and galls on the roots were counted. S. torvum was resistant to M. incognita, Mi-1 virulent M. incognita, M. javanica, M. arenaria and M. luci, but susceptible to M. hapla. In Turkey, S. torvum has commonly been used as a rootstock against Meloidogyne spp. The study provided background information of S. torvum rootstock resistance to the mentioned populations of root-knot nematodes, except M. hapla.

Screening and identification of cucumber germplasm and rootstock resistance against the root-knot nematode (Meloidogyne incognita).

Root-knot nematodes (Meloidogyne spp) are destructive agricultural pests that reduce the productivity of cultivated vegetables worldwide, especially when vegetables are cropped continuously in greenhouses. Cucumbers (Cucumis sativus L.), in particular, suffer extensive damage due to root-knot nematodes, and only a few wild species are known to be resistant. Grafting of cultivated plants to rootstocks of known resistant germplasms could be an effective method to resolve this problem. In this study, 21 cucumber germplasms and seven rootstocks were evaluated for resistance based on the growth of cucumber seedlings and resistance indexes to Meloidogyne incognita, which were surveyed 25 days after inoculation with M. incognita. Cluster analysis and principal component analysis (PCA) were used to investigate the resistance of 21 cucumber germplasms and seven rootstocks based on their growth and resistance indexes after inoculation with M. incognita. These analyses showed that the 21 germplasms and seven rootstocks could be divided into three groups based upon their resistance levels: moderately resistant, susceptible, and highly susceptible to M. incognita. All 21 cucumber germplasms exhibited susceptibility or high susceptibility to M. incognita and most rootstocks exhibited moderate resistance. The PCA results were consistent with those of the clustering analysis. The Jinyou No.1 cultivar had the highest resistance to M. incognita among the 21 cucumber germplasms, and Huangzhen No.1 cultivar had the highest resistance among the seven rootstock cultivars.

Systemic resistance in citrus to Tetranychus urticae induced by conspecifics is transmitted by grafting and mediated by mobile amino acids.

Recent research suggests that systemic signalling and communication between roots and leaves plays an important role in plant defence against herbivores. In the present study, we show that the oviposition of the two-spotted spider mite Tetranychus urticae in the systemic leaves of citrus rootstock Citrus aurantium (sour orange) was reduced by 50% when a lower leaf was previously infested with conspecifics. Metabolomic and gene expression analysis of the root efflux revealed a strong accumulation of glutamic acid (Glu) that triggered the expression of the citrus putative glutamate receptor (GRL) in the shoots. Additionally, uninfested sour orange systemic leaves showed increased expression of glutamate receptors and higher amounts of jasmonic acid (JA) and 12-oxo-phytodienoic acid in plants that were previously infested. Glu perception in the shoots induced the JA pathway, which primed LOX-2 gene expression when citrus plants were exposed to a second infestation. The spider mite-susceptible citrus rootstock Cleopatra mandarin (C. unshiu) also expressed systemic resistance, although the resistance was less effective than the resistance in sour orange. Surprisingly, the mobile signal in Cleopatra mandarin was not Glu, which suggests a strong genotype-dependency for systemic signalling in citrus. When the cultivar Clemenules (C. clementina) was grafted onto sour orange, there was a reduction in symptomatic leaves and T. urticae populations compared to the same cultivar grafted onto Cleopatra mandarin. Thus, systemic resistance is transmitted from the roots to the shoots in citrus and is dependent on rootstock resistance.

Apple rootstock resistance to drought

Water for irrigation will likely be less available in apple-growing regions due to climate change and competition with human needs other than agriculture. Apple cultivars and rootstocks may differ in water use necessary for acceptable cropping. In two greenhouse experiments in 2014 and 2015 rootstocks (M.9 and MM.111) and scions (‘Gala’ and ‘Fuji’) with known differences in size control and potential resistance to drought were compared under conditions of reduced water availability. After 1 week without irrigation in 2014 the potting soil moisture and leaf water potential (ΨL) were reduced more in trees on MM.111 than M.9 rootstocks and by ‘Gala’ than ‘Fuji’ scions. Abscisic acid (ABA) and associated metabolites dihydrophaseic acid, abscisic acid glucose ester, and phaseic acid generally were greater for both scions on M.9 than MM.111. Concentrations of ABA metabolites were greater in ‘Gala’ than ‘Fuji’ suggesting significant metabolic rates in leaves. As noon ΨL decreased between −1.5 and −2.0MPa leaf ABA levels increased exponentially to concentrations above 500ng/g dw and stomatal conductance (gs) decreased to less than 50 mmole H2O m−2s−1. At reduced gs carbon assimilation (A) was low but greater in trees on M.9 than on MM.111. Trees grown on M.9 partitioned less dry weight (dw) to roots than MM.111. However the% dw partitioned to fine roots was greater in M.9 than MM.111 which may have helped trees grow in a small environment such as a pot. In 2015 trees were grown in 45- and 75-L pots and irrigated over 3 weeks to maintain a steady ΨL between −1.5 and −2.5MPa. This longer-term water stress in 2015 resulted in greater gs and A in trees on MM.111 and in larger pots but WUE was still greater in trees grafted to M.9 in 3 of the 5 drought dates measured. Both rootstocks provided drought resistance, but by mechanisms which appear to differ and which may provide benefits to apple trees grown with reduced irrigation or with water stress. The dwarfing rootstock M.9 produces higher levels of ABA that may regulate stomatal opening and improve short-term drought resistance. The more invigorating rootstock MM.111 may be drought hardy in the longer-term due to development of a more extensive root system.

Evaluating Grafted Watermelon for Verticillium Wilt Severity, Yield, and Fruit Quality in Washington State

Verticillium wilt caused by Verticillium dahliae is a serious disease for watermelon growers in Washington State. Grafting represents a possible alternative disease management strategy, but little is known about rootstock resistance to verticillium wilt or the performance of grafted watermelon in the different production regions of the state. In this study, verticillium wilt severity, yield, and fruit quality were evaluated at three contrasting field sites in Washington using verticillium wilt-susceptible ‘Sugar Baby’ (diploid) watermelon grafted onto four commercial rootstock cultivars (Marvel, Rampart, Tetsukabuto, and Titan); nongrafted ‘Sugar Baby’ was included as the control. Verticillium dahliae soil densities varied at each site (<1.0, 5.7, and 18.0 colony-forming units (cfu)/g soil at Othello, Eltopia, and Mount Vernon, respectively). Area under disease progress curve (AUDPC) values differed significantly among treatments at Eltopia and Mount Vernon. Nongrafted ‘Sugar Baby’ had the highest AUDPC value at all three sites, while ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had the lowest AUDPC value at Eltopia and Mount Vernon. Nongrafted ‘Sugar Baby’ also had the lowest fruit weight per plant at all sites, but ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had the highest fruit weight per plant at Eltopia and Mount Vernon. Marketable fruit weight per plant did not differ among treatments at Othello. Yield was negatively correlated with AUDPC values at both Eltopia and Mount Vernon. Fruit number per plant was only significantly impacted at Eltopia, where ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had more fruit per plant than all other treatments except ‘Sugar Baby’ grafted onto ‘Rampart’. Fruit quality (flesh firmness, total soluble solids, and lycopene content) was unaffected by grafting at either Othello or Eltopia, except for increased flesh firmness for ‘Sugar Baby’ grafted onto ‘Marvel’ and ‘Titan’ as compared with nongrafted ‘Sugar Baby’ at Eltopia. At season’s end, plants were sampled from all treatments at Eltopia and Mount Vernon and assayed for V. dahliae. Microsclerotia typical of this organism were observed in all samples. Results from this study indicate that verticillium wilt of watermelon can be successfully managed by grafting when the V. dahliae soil density exceeds 5.0 cfu/g in Washington. In addition, grafting does not reduce fruit quality and using certain rootstocks can improve the quality of flesh firmness at certain locations.

Greenhouse Evaluation of Melon Rootstock Resistance to Monosporascus Root Rot and Vine Decline as Well as of Yield and Fruit Quality in Grafted ‘Inodorus’ Melons

Melons (Cucumis melo L.) are generally grafted onto Cucurbita rootstocks to manage soilborne pathogens such as Monosporascus root rot and v ine decline (MRR/VD) and Fusarium wilt. However, g rafting onto Cucurbita rootstocks reportedly results in the reduction of fruit quality. In this study, the resistance to MRR/VD, yield, and fruit quality of melons grafted onto melon rootstocks were evaluated under greenhouse conditions. Eight melon rootstocks (R1 to R8) were used and the inodorus melon 'Homerunstar' was used as scion. Melon rootstocks R1 to R6 were selected based on resistance to MRR/VD under greenhouse conditions. Non-grafted 'Homerunstar' and plants grafted onto squash interspecific hybrid 'Shintozwa' rootstock (Cucurbita maxima D. <TEX>${\times}$</TEX> C. moschata D.) served as controls. Grafted melons were cultivated in the greenhouse infested with Monosporascus cannonballus during two growing seasons (summer and autumn). The responses to MRR/VD, yield, and fruit quality differed depending on the rootstocks and growing season. The melons grafted onto 'Shintozwa' exhibited less severe disease symptoms and higher survival rates than non-grafted melons in both seasons. While the melon rootstocks in the summer cultivation did not increase the survival rate compared to non-grafted melons, the melon rootstocks R1 and R2 in the autumn cultivation led to higher survival rates. The melon rootstocks resistant to MRR/VD increased the percentage of marketable fruits and marketable yields. Grafting onto the melon rootstocks caused little or no reduction of fruit quality such as low calcium content, fruit softening, and vitrescence, especially in lower-temperature autumn season. Accordingly, these results suggest that grafting onto the melon rootstocks may increase the tolerance to MRR/VD and the marketable yield without a reduction of fruit quality.

Resistência de pimentas a nematóides de galha e compatibilidade enxerto/porta-enxerto entre híbridos de pimentão e pimentas

Avaliou-se a resistência à Meloidogyne incognita e a compatibilidade de enxertia de treze porta-enxertos de pimenta (nove Capsicum chinense; três C. annuum e um C. frutescens) quando enxertados com os híbridos de pimentão-vermelho Rubia R, Margarita e Maximos. O experimento foi conduzido em 2005 na UNESP-FCAV em Jaboticabal-SP. As plantas foram enxertadas por garfagem do tipo fenda simples e, 25 dias após foram avaliadas quanto à percentagem de "pegamento" e, posteriormente, juntamente com plantas sem enxertia, foram transplantadas em casa de vegetação e inoculadas, individualmente, com 5.000 ovos e juvenis de segundo estádio de M. incognita. A avaliação da resistência dos porta-enxertos ao nematóide foi feita aos 181 dias após a inoculação, com base no fator de reprodução; a avaliação da compatibilidade enxerto/porta-enxerto foi realizada levando em consideração a produtividade e a qualidade dos frutos obtidas em sete colheitas, realizadas entre 113 e 181 dias após o transplante das mudas. Aos 25 dias após a enxertia, para todos os tratamentos, em média, 99,69% das plantas enxertadas apresentavam-se com "pegamento". Os porta-enxertos C. annuum e C. frutescens, ao final do ciclo de cultivo, foram resistentes à M. incognita e proporcionaram nas plantas enxertadas, respectivamente, as maiores e menores produtividades e qualidades de frutos, sendo designados de compatíveis e incompatível para enxertia com os híbridos de pimentão-vermelho Rubia R, Margarita e Maximos. 'Maximos' e 'Margarita' quando enxertados apresentaram melhor produtividade e qualidade de frutos do que 'Rubia R'; quando sem enxertia não diferiram em produtividade, havendo destaque para 'Margarita' quanto à qualidade dos frutos.

Evaluation of Rootstock Resistance to Fusarium Wilt and Gummy Stem Blight and Effect on Yield and Quality of a Grafted ‘Inodorus’ Melon

Grafting represents an effective tool for controlling the race 1,2 of Fusarium oxysporum f. sp. melonis (FOM) and Didymella bryoniae in melon (Cucumis melo L.). Although not considered a soilborne pathogen, D. bryoniae survives on plant remains in the soil. The lack of effective resistant commercial hybrids and the gradual reduced use of soil fumigation with methyl bromide increase the risk of damages by both these pathogens. We determined the effectiveness of eight commercial rootstocks, ‘RS 841’, ‘P 360’, ‘ES 99-13’, ‘Elsi’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne), and ‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’ (Cucumis melo genotypes), for their resistance to FOM and D. bryoniae. During 2003 and 2004 growing seasons, the inodorus F1 hybrid Incas was grafted onto each of these commercial rootstocks and then evaluated, under greenhouse conditions, in terms of productivity and fruit quality. Cucurbita rootstocks (‘RS 841’, ‘P 360’, ‘ES 99-13’, ‘Elsi’) were highly resistant both to the race 1,2 of FOM (100% survival) and to D. bryoniae (almost absent crown lesions and low leaf disease index); this reaction clearly differed from that of both the C. melo rootstocks (‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’) and the control Incas. In both years, the highest yield was recorded in the graft combination Incas/‘RS 841’ with 5.6 and 8.1 kg·m−2 during 2003 and 2004, respectively. The Cucurbita rootstock ‘RS 841’ produced yields higher than C. melo rootstocks (‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’) and the control Incas. Fruit dry matter, titratable acidity, total soluble solid contents, fruit firmness, and Hunter color [L* (brightness), a* (redness), and b* (yellowness) parameters] of grafted melons were similar to those of the plants grown on their own roots.

Rootstock resistance to Fusarium wilt and effect on watermelon fruit yield and quality

The potential of grafted watermelon for resistance toFusarium oxysporum f.sp.niveum on some Curcurbitaceae,Lagenaria, Luffa, Benincasa and commercial rootstocks was evaluated. Effects of grafting on yield and quality of diseased plants were evaluated. All grafted plants and rootstocks were resistant to the three known races (0, 1, and 2) ofF. oxysporum f.sp.niveum except watermelon cv. ‘Crimson Tide’, which was susceptible to race 2. Fruit yield was positively (21–112%) affected byLagenaria rootstocks but negatively affected (200–267%) byCucurbita rootstocks when compared with the control. While only minor differences in fruit quality were determined in control and grafted plants onLagenaria rootstocks, the quality parameters for watermelon grafted ontoCucurbita rootstocks were lower than in the control. The reasons for low yield and quality might be due to an incompatibility betweenCucurbita rootstocks and watermelon. These results showed that rootstock influence on disease resistance as well as yield and quality of scion fruit is important in determining the potential use of grafting applications in watermelon.

Host Selection and Root Colonization of Cyanogenic Stonefruit Species by &lt;I&gt;Capnodis&lt;/I&gt; spp. (Coleoptera: Buprestidae)

The host selection by adults of two flatheaded rootborers Capnodis tenebrionis L. and C. carbonaria Klug was investigated by examinination of their preference for feeding and oviposition among some of their major host tree taxa. We also studied the resistance to both Capnodis spp. of 10 Prunus rootstocks that were being challenged with the buprestid neonates. The scion selection for feeding and oviposition was related to the cyanide potential in the twig cortex; while potential rootstock resistance was related to the amount of the cyanogenic glycosides in the rootstock cortex. Plum and apricot were preferred by C. tenebrionis and peach was preferred by C. carbonaria. All Prunus rootstocks tested were colonized to some extent by both species. Partial correlation was found between cyanide potential and oviposition for C. carbonaria but not for C. tenebrionis. Nor was significant correlation found between cyanide potential and host preference for feeding by both species. Peach and plum, which displayed the highest level of cyanide potential, were also the preferred by both species for feeding and oviposition. Apple, with the lowest cyanide potential, was the least preferred for both activities. We found an inverse relationship between resistance to Capnodis and level of cyanogenic compounds in the root cortex. Adults of both Capnodis spp. were not deterred by high levels of cyanogenic compounds in the scion twig cortex. Our findings suggest that cyanide potential is not a reliable indicator of the degree of resistance in Prunus spp. rootstocks to Capnodis spp.

Resistance of Geneva and Other Apple Rootstocks to Erwinia amylovora.

When vigorously growing shoots of 49 different apple rootstocks grown in a greenhouse were inoculated with different strains of Erwinia amylovora, Budagovsky 9 (B.9), Ottawa 3, Malling 9, and Malling 26 were the most fire blight susceptible rootstocks and Geneva 11, Geneva 65, Geneva 16, Geneva 30, Pillnitzer Au51-11, Malling 7, and several breeding selections were the most resistant. Significant strain-rootstock interactions were observed in the amount of fire blight that resulted from inoculation. Field-grown fruiting 'Royal Gala' trees on Geneva 16 and Geneva 30 rootstocks were highly resistant to rootstock infection (no tree mortality) when trees sustained severe blossom infection with E. amylovora, compared with Malling 9 and Malling 26 rootstock clones, which were highly susceptible to infection (36 to 100% tree mortality). In contrast to potted own-rooted B.9 plants inoculated in a greenhouse, B.9 rootstocks of orchard trees appeared resistant to rootstock infection (0% tree mortality). Orchard trees on Geneva 11 were moderately resistant to rootstock infection (25% tree mortality). There was general agreement in the evaluation of resistance under orchard conditions when rootstock resistance was evaluated in relation to controlled blossom inoculation or to natural blossom infection.

Susceptibility of Austrian apricot and peach cultivars to

1548 stone fruit trees (1435 trees of P. armeniaca, 113 trees of P. persica) were examined by PCR for ESFY to get information on spread and susceptibility of cultivars and rootstocks used in Austrian stone fruit production. Cultivar susceptibility seems to be less important for tolerance to ESFY than rootstock resistance. Apricot cultivars on rootstocks of myrobalan, commonly used in Austria, are more infected than cultivars on plum rootstocks. Data on peach and apricot rootstocks are not representative as both are not commonly used in Austrian apricot production. In addition, the presence of peroxidase activity in shoot sieve tubes of infected apricot trees (Hungarian Best) reveals that peroxidase is involved in defense mechanisms in plant-pathogen interaction.