Susceptible Cv Research Articles

Defense response of seedling plumule and mesocotyl of sorghum to infection by Sporisorium sorghi, causing covered kernel smut in relation to disease resistance classes

Susceptibility of sorghum seedlings to infection by Sporisorium sorghi, the fungus causing covered kernel smut (CKS) disease, is limited to the period between the sowing of the seed and emergence of the seedling. Microscopy and PCR diagnosis of 7-day-old infected seedlings detected hyphae of S. sorghi in plumule and mesocotyl tissue but not in coleoptile and radicle tissue. Percent infected seedling plumule and mesocotyl tissue detected by microscopy and PCR corresponded well to field resistance classes for CKS in mature panicles of both sorghums tested with Giza-15 being highly susceptible and hybrid Shandweel-305 being resistant. Bulk extracts of phenolics and antioxidants from seedling plumule and mesocotyl tissues of hybrid Shandweel-305 cv significantly inhibited the in vitro mycelial growth of S. sorghi more than those from Giza-15 cv. Moreover, bulk extracts of plumule and mesocotyl tissue of seedlings grown from seed inoculated with S. sorghi teliospores contained higher phenolic and antioxidant content in the resistant hybrid (Shandweel-305) than the highly susceptible cultivar (Giza-15). Similarly, bulk extracts of plumule and mesocotyl tissue of 7-day-old seedlings grown from seed inoculated with S. sorghi teliospores contained higher phenolic and antioxidant content in the resistant hybrid (Shandweel-305) than the highly susceptible cultivar (Giza-15). Ferulic, isorhamnetin and kaempferol acids were detected only in plumule and mesocotyl tissue of resistant hybrid Shandweel-305, whereas ellagic, fumaric and vanillic acids were detected only in highly susceptible Giza-15 cv. Ferulic acid added to malt dextrose broth medium significantly inhibited in vitro teliospore germination and mycelial growth of S. sorghi, especially when added at the highest concentrations. This research established that the mode of seedling infection of sorghum by S. sorghi is almost exclusively through the plumule and mesocotyl tissue. Within these tissues, the presence of the pathogen can induce host production of phenolics, including the fungitoxic ferulic acid and antioxidants at higher concentrations within the resistant sorghum than in the highly susceptible cultivar.

Application of sodium salicylate up-regulates defense responseagainst Fusarium graminearum in wheat spikes

Fusarium head blight caused by the hemibiotrophic fungus Fusarium graminearum is one of the most devastating diseases of wheat which reduces both grain yield and quality. To better understand mechanism underlying wheat resistance to this pathogen, the expressions of five candidate genes encoding phenylalanine ammonia-lyase (PAL), glucanase-2 (Gl 2), class IV chitinase (Cht-4), cytochrome P450 (CYP), and pleiotropic drug resistance (PDR) following spike inoculation with F. graminearum was compared in susceptible cv. Falat and resistant cv. Sumai3 at three time points (48, 96, 144 h after inoculation). Real-time quantitative PCR analysis indicated earlier and greater inductions of PAL, Glu-2, and Cht-4 in spikes of 'Sumai3' as compared to 'Falat' in response to F. graminearum inoculation. The expression of CYP in the resistant 'Sumai3' was about three times higher than in 'Falat' at 144 h after pathogen inoculation. Moreover, soil drench application of sodium salicylate (SA) one day before pathogen inoculation drastically curtailed pathogen infection in both the cultivars. Furthermore, SA treatment caused an induction of these genes in spikes of the susceptible cultivar to show a similar pattern as in the resistant one when inoculated with F. graminearum. Proteomics analysis of F. graminearum treated spikes 96 h after inoculation confirmed an increase of Glu and Cht spot volume in 'Sumai3' whereas a decrease in 'Falat'. The SA treatment also caused significant increases in Glu and Cht spot volumes in both the cultivars. Our findings show an association between SA improvement of wheat defense against F. graminearum infection and induction of genes encoding proteins involved in pathogen response (Glu-2, Cht-4), secondary metabolite biosyntheses (PAL), and xenobiotic detoxification (CYP and PDR).

Seed tuber incidence, identification and pathogenicity of Verticillium species infecting potatoes in South East Australia

Verticillium wilt, caused by the soilborne fungi Verticillium dahliae and Verticillium albo-atrum, is a serious disease of potato as well as many other crops. Potato seed tuber surveys (2010 to 2012) from Victoria and Tasmania, Australia identified V. dahliae, V. albo-atrum and V. tricorpus infecting the stem end vascular tissue of seed tubers. The species were identified by traditional morphology and phylogenetic analysis of the ITS region. Isolation of V. dahliae within a seed lot varied greatly and ranged from 0 to 55%. Verticillium spp. were isolated from the stem-end vascular tissue of tubers from seed lots from Victoria and Tasmania with an overall percent infection of 27.7 (V. dahliae), 8.4 (V. albo-atrum) and 4.8 (V. tricorpus). Verticillium dahliae was isolated from 11% of tubers with discoloured stem-end vascular tissue and 3.3% of tubers without stem-end vascular decolourisation suggesting that tuber stem end vascular discolouration symptoms were not a reliable indication of Verticillium wilt infection. In glasshouse trials, V. dahliae isolates from different geographical locations varied in pathogenicity during infection of susceptible potato cv Shepody, moderately resistant cv Ranger Russet and eggplant cv Black Beauty. The majority of V. dahliae isolates were highly aggressive in potato and eggplant, especially the Tasmanian V. dahliae isolates. Infected plants of cv Shepody inoculated with V. albo-atrum and V. tricorpus showed typical wilt symptoms however, the severity of infection caused by V. tricorpus was substantially lower compared to highly aggressive isolates of V. dahliae. In eggplant, V. dahliae isolates also varied in pathogenicity in terms of disease severity but all isolates significantly (p ≤ 0.05) reduced eggplant growth.

Identification of two endophytic fungi that control Septoria tritici blotch in the field, using a structured screening approach

We applied a structured screening approach to identify biocontrol agents (BCAs) against the wheat disease Septoria tritici blotch (STB) caused by Zymoseptoria tritici, with potential for commercial use. A limitation of many screening programmes is that BCAs with an effect in vitro do not necessarily show an effect in planta. Therefore, we relied on in planta screening and aimed to optimise host and environmental compatibility of the BCAs by isolating endophytic fungi from the plant, tissue and environment of future application. Furthermore, in planta screening was complemented by a small-scale field experiment and in vitro characterisation (temperature requirements, sporulation potential and fungicide tolerance) as well as a literature search, to identify the most promising isolates.The screening approach resulted in identification of two promising fungal strains that significantly and reliably reduced STB in the highly susceptible wheat cv. Sevin by up to 75% under controlled conditions. Significant reductions of disease were also observed under field conditions in cv. Mariboss. While further validation in the field is required, the two endophyte isolates, Penicillium olsonii ML37 and Acremonium alternatum ML38, have the potential for implementation in integrated disease management strategies using both fungicides and BCAs, because of their tolerance to the fungicide prothioconazole-desthio. Integrated approaches, combining different agents, offer a more sustainable and durable way to control STB. They would allow the reduction of fungicide inputs and thus help reduce the development of fungicide resistance in the pathogen population.

Impact of Colletotrichum acutatum Pathogen on Olive Phenylpropanoid Metabolism

Olive anthracnose caused by the hemibiotrophic fungal pathogen Colletotrichum acutatum is a serious threat to the olive sector. Olive oil and fruit production is severely constrained by Colletotrichum spp. infection, being C. acutatum the most distributed pathogen in Portuguese olive orchards. To understand the impact of C. acutatum on phenylpropanoids biosynthesis, the enzyme activity, phenolic compounds, ortho-diphenols, and flavonoids content were determined and correlated with the expression of gene encoding key enzymes within phenylpropanoids metabolism in susceptible and tolerant olive fruits, during maturation and when infected with C. acutatum. Differences between cultivars was observed, the tolerant olive cv. Picual presented a higher basal value and a stable phenolic content throughout the infection process, supporting its high C. acutatum tolerance, whereas in the susceptible olive cv. Galega these secondary metabolites were significantly increased only after the elicitation with C. acutatum.

Botrytis cinerea differentially induces postharvest antioxidant responses in 'Braeburn' and 'Golden Delicious' apple fruit.

BACKGROUNDThe fruit of two apple cultivars – ‘Braeburn’, which is susceptible to inoculation with Botrytis cinerea, and the less susceptible cv. ‘Golden Delicious’ – were investigated with respect to their response to inoculation with B. cinerea. Successful infection by B. cinerea leads to an oxidative burst and perturbation of plant redox homeostasis. To investigate the interaction between apple fruit and B. cinerea, antioxidant metabolism in fruit samples from sun‐exposed and shaded sides of different tissue types was measured over time.RESULTSThe sun‐exposed tissue of ‘Braeburn’ had higher initial levels of total vitamin C in the peel and phenolic compounds in the flesh than ‘Golden Delicious’, despite its greater susceptibility to gray mold. A substantial antioxidant response was recorded in diseased ‘Braeburn’ fruit 14 days after inoculation, which involved an elevated superoxide dismutase activity and ascorbate peroxidase activity, a progressive oxidation of total vitamin C, and a decrease in peroxidase activity and phenolic content. Disease development was slower on the sun‐exposed sides than on the shaded sides.CONCLUSIONThe two cultivars appeared to utilize different strategies to defend themselves against B. cinerea. ‘Golden Delicious’ almost entirely escaped infection. Preharvest exposure of apple fruit to high light / temperature stress appears to prepare them to better resist subsequent postharvest attack and disease. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The OmpA Gene of Xanthomonas axonopodis pv. glycines is Involved in Pathogenesis of Pustule Disease on Soybean.

The goal of this study was to elucidate the role of the outer membrane protein A (ompA) gene of Xanthomonas axonopodis pv. glycines in bacterial pustule pathogenesis of soybean. An ompA mutant of X. axonopodis pv. glycines KU-P-SW005 was shown to significantly decrease cellulase, pectate lyase, and polysaccharide production. The production of these proteins in the ompA mutant was approximately five times lower than that of the wildtype. The ompA mutant also exhibited modified biofilm development. More importantly, the mutant reduced disease severity to the soybean. Ten days after inoculation, the virulence rating of the susceptible soybean cv. SJ4 inoculated with the ompA mutant was 11.23%, compared with 87.98% for the complemented ompA mutant. Production of cellulase, pectate lyase, polysaccharide was restored, biofilm, and pustule numbers were restored in the complemented ompA mutant that did not differ from the wild type. Taken together, these data suggest that OmpA-mediated invasion plays an important role in protein secretion during pathogenesis to soybean.

Response of two Citrullus amarus accessions to isolates of three species of Meloidogyne and their graft compatibility with watermelon

The response of two Citrullus amarus accessions, BGV0005164 and BGV0005167, was assessed against different Meloidogyne arenaria, Meloidogyne incognita, and Meloidogyne javanica isolates in pot experiments and against M. incognita in plastic greenhouse. In the pot experiments, plants were inoculated with a second-stage juvenile per cm3 of sterile sand and maintained in a growth chamber at 25 °C for 50 days. The watermelon cv. Sugar Baby was included as a susceptible control for comparison. At the end of the experiments, the number of egg masses and eggs per plant was determined, and the reproduction index was calculated as the percentage of the number of eggs produced in the C. amarus accessions with regard to that produced in the susceptible cv. Sugar Baby. In the plastic greenhouse experiment, the ungrafted watermelon cv. Sugar Baby and watermelons grafted onto each of the C. amarus accessions and onto the watermelon rootstock cv. Robusta were cultivated from May to August 2016 in plots with nematode densities from 46 to 1392 J2 per 250 cm3 of soil at transplantation. At the end of the experiment, the galling index and the number of eggs per plant were determined, and the reproduction index was calculated. Additionally, the compatibility of the two accessions with the watermelon cv. Sugar Baby and the effect on fruit quality (weight, size, shape, firmness, pH, total soluble solids, and flesh color) were assessed under a hydroponic system in a greenhouse. The commercial rootstocks cv. Cobalt and cv. Robusta were also included. All the Meloidogyne isolates produced less egg masses and eggs per plant on the accessions than on Sugar Baby. Both accessions performed as resistant against M. arenaria, and from highly to moderately resistant to M. incognita and M. javanica in pot experiments. In the plastic greenhouse experiment, both C. amarus accessions performed as resistant to M. incognita. Both C. amarus accessions were compatible with the watermelon cv. Sugar Baby, but only the BGV0005167 accession did not influence the fruit quality. Then, the BGV0005167 accession is a promising rootstock for managing the three tropical root-knot nematode species without influencing watermelon fruit quality.

Phytophthora sojae zoospores differ in chemotaxis to the root and root exudates of host soybean and nonhost common bean

Phytophthora root and stem rot of soybean is a destructive disease in many countries caused by the soil-borne pathogen Phytophthora sojae. The interaction between soil-borne pathogens and plant roots before invasion is a focus of interest for revealing host and nonhost resistance mechanisms to soil-borne pathogens. In the present study, soybean cvs. Sloan (susceptible), Williams 82 (resistant) and nonhost common bean cv. Yidianhong were used to determine the effect of roots, root exudates, and isoflavones, amino acids, sugars, and citric acid from the root exudates on the pre-infection behavior (taxis, encystment and cyst germination) of zoospores of P. sojae. The elongation zone of roots of both host soybeans attracted significantly more zoospores than did that of the nonhost bean, and that of the susceptible cultivar attracted significantly more zoospores than did that of the resistant cultivar. Similarly, the host soybean root exudates attracted zoospores and promoted zoospore encystment and cyst germination, but nonhost root exudates had no effect on zoospores. Thus, P. sojae apparently selects its host depending on the root exudates. Of the 26 total components detected from root exudates, the exudates from susceptible and resistant soybeans and nonhost common bean had 12, 17, and 25 components respectively. The differences between the host and nonhost were mainly in the type and concentration of amino acids. Most components were significant chemoattractants of P. sojae zoospores. However, when these attractants were mixed at their relative concentrations in the root exudates, the chemoattraction was significantly reduced compared to that of the sum of each components, and the reduction from strongest to weakest was nonhost common bean, resistant and susceptible soybeans, indicating that these components in the root exudates interact with each other, and the intensity of the interaction relates to the type and concentration of the components. This phenomenon is because some components may share the same receptor, thus causing an obstructive effect. This result may also be a reason that common bean is a nonhost of P. sojae. In addition, the relative local concentrations of citric acid in the root exudates of both nonhost cv. Yidianhong and resistant cv. Williams 82 were repellent to zoospores of P. sojae. Root exudates of susceptible cv. Sloan amended with two concentrations of citric acids especially reduced zoospore chemoattraction, indicating that citric acid in the root exudates also plays an important role in host and nonhost resistance to P. sojae.

Cucumis metuliferus reduces Meloidogyne incognita virulence against the Mi1.2 resistance gene in a tomato-melon rotation sequence.

Susceptible tomato cv. Durinta, ungrafted or grafted onto cv. Aligator resistant rootstock, both followed by the susceptible melon cv. Paloma, ungrafted or grafted onto Cucumis metuliferus BGV11135, and in the reverse order, were cultivated from 2015 to 2017 in the same plots in a plastic greenhouse, infested or not with Meloidogyne incognita. For each crop, soil nematode densities, galling index, number of eggs per plant and crop yield were determined. Virulence selection was evaluated in pot experiments. In the tomato-melon rotation, nematode densities increased progressively for the grafted tomato, being higher than for ungrafted plants at the end of the study; this was not the case in the melon-tomato rotation. Grafted crops yielded more than ungrafted crops in the infested plots. Virulence against the Mi1.2 gene was detected, but not against C. metuliferus. Reproduction of M. incognita on the resistant tomato was ∼ 120% that on the susceptible cultivar after the first grafted tomato crop, but this decreased to just 25% at the end of the experiment. Alternating different resistant plant species suppresses nematode population growth rate and yield losses. Although this strategy does not prevent virulence selection, the level was reduced. © 2018 Society of Chemical Industry.

English

Banana, a major staple in East and Central Africa is constrained by banana Xanthomonas wilt (BXW) caused by Xanthomonas campestris pv. musacearum (Xcm). Xcm-infected plants are rapidly destroyed leading to 100% yield loss. Cultural controls are effective but laborious attracting laxity among farmers. This has led to epidemic resurgence in areas where BXW had been contained hence spread to new regions. Reliable control option would be planting Xcm-resistant varieties but extensive germplasm evaluation for their identification has not been conducted. Objective therefore was to determine existence of Xcm-resistance in banana by evaluating major banana cloneset representatives among indigenous cultivars plus introduced foreign Musa accessions. Potted plants were artificially inoculated with 0.5 ml (108CFU) of Xcm suspension. Promising selections from pot trial were later evaluated under natural transmission in field. Field trial plants were infected via insect vectors from spreader plants of highly susceptible cv Kayinja infected by spraying flowers with Xcm. Severity of Xcm-infection was semi-quantified using scales 1-5 and 0-5 for pot and field screening trials respectively. This enabled calculation of disease index as a measure of resistance for each genotype. High index implied highly susceptible banana genotype and low index resistant genotype. Findings 44 days after artificial inoculation showed wild banana M. balbisiana had 0.0 disease index thus highly resistant. All other banana genotypes tested under similar conditions had disease index of 100 thus susceptible. In field (insect vector transmission), disease index varied significantly among various genotypes evaluated, some susceptible while others; M. balbisiana, Mbwazirume, M9 and M. Zebrina resistant throughout 360 days of observation. We recommend that heritable traits that confer resistance in M. balbisiana, Mbwazirume, M9 and M. zebrina to Xcm be identified for utilization in genetic modification of farmer preferred bananas. Varieties Mbwazirume and M9 should be promoted for farmer growing to complement cultural controls against BXW. Key words: Xanthomonas campestris pv. musacearum, banana Xanthomonas wilt, banana.

Reproduction and life history traits of a resistance breaking Globodera pallida population

Abstract The main and most efficient measure to control potato cyst nematode (PCN) is the use of resistant cultivars. German and Dutch National Plant Protection Organizations (NPPOs) recently reported the emergence of Globodera pallida populations virulent on potato cultivars carrying resistance against pathotype 2/3. The development and virulence of the virulent population Oberlangen from Germany in comparison to the reference population G. pallida Pa3 Chavornay were investigated on resistant and susceptible cultivars in glasshouse experiments. Various life history traits associated with change in virulence were also assessed. Hatching of second-stage juveniles (J2s) was similar for both populations but incubation of cysts in potato root diffusate resulted in higher hatching rates compared to 3 mM Zinc Chloride and tap water. Both populations showed high penetration rates in the roots of the resistant and susceptible cultivars. However, only the population Oberlangen was able to complete the life cycle in the roots of the resistant potato cultivar. In ‘Seresta’, the resistance response restricted the formation of females by avirulent individuals in favor of males. Oberlangen was virulent on all cultivars tested. No difference in cyst size, number of eggs per cyst, length of juveniles, and males was found for Oberlangen and Chavornay on the susceptible cv. ‘Desiree’. However, cysts of virulent populations from the same region Oberlangen was obtained from had a significantly larger diameter compared to avirulent populations. The population Oberlangen showed a higher reproduction and fitness than the reference population Chavornay on susceptible cultivars and could serve as a future reference population in testing of new potato cultivars for resistance against this new virulence type in Europe.

Increased virulence of Globodera pallida during repeated rearing on different resistant potato cultivars explained by a simple model

Selection for virulence of Globodera pallida on potato cultivars was studied for four generations under controlled conditions. The reproduction rate (Pf/Pi) of a mixed Pa2/3 population increased by a factor of 61 during rearing on the partially resistant potato cv. Darwina compared to rearing on the susceptible cv. Irene. This was a result of selection for virulence on cv. Darwina, and achieving the Hardy–Weinberg equilibrium on cv. Irene. Increased virulence also significantly raised the reproduction rate on several other Solanum genotypes. These changes could be explained reasonably well by the monogenic inheritance of a virulence factor breaking the Grp1 locus. The virulence changes were probably mainly evoked by this gene only, inherited from S. vernei 1‐3 or S. vernei 24/20. The Grp1 locus has probably provided the differential S. vernei hybrid (VTn)2 62‐33‐3 with its resistance to the Pa2 group and not to the Pa3 group. Alternation of cultivars did not halt selection if the cultivars highly differentiated between the Pa2 and Pa3 populations. Only when alternation was with cultivars that harboured a different resistance gene against Pa3 was selection for virulence delayed. Differences in virulence levels (i.e. reproduction rates) within the nematode population determined the rate of selection, not the resistance level itself. Selection of a Pa3 population for three generations on cv. Karakter not only increased the reproduction rate on cv. Karakter itself by a factor 4.2, but also raised the reproduction on other potato genotypes. A simple monogenic model could explain these changes in virulence.

Er3 gene, conferring resistance to powdery mildew in pea, is located in pea LGIV

Three genes for resistance to Erysiphe pisi, named er1, er2 and Er3 have been described in pea so far. er1 gene is located in pea linkage group VI, while er2 gene has been mapped in LGIII. SCAR and RAPD markers tightly linked to Er3 gene have been identified, but the position of these markers in the pea genetic map was unknown. The objective of this study was to localize Er3 gene in the pea genetic map. Towards this aim, the susceptible pea cv. Messire (er3er3) and a resistant near isogenic line of Messire (cv. Eritreo, Er3Er3) were surveyed with SSRs with known position in the pea map. Three SSRs were polymorphic between ‘‘Messire’’ and ‘‘Eritreo’’ and further surveyed in two contrasting bulks formed by homozygous Er3Er3/er3er3 individuals obtained from a F2 population derived from the cross C2 (Er3Er3) 9 Messire (er3er3). A single marker, AA349, was polymorphic between the bulks. Subsequently, other ten markers located in the surrounding of AA349 were selected and analysed in Er3Er3 and er3er3 plants. As a results, another SSR, AD61, was found to be polymorphic between Er3Er3 and er3er3 plants. Further linkage analysis confirmed that SSRs AA349 and AD61 were linked to Er3 and to the RAPD and SCAR markers previously reported to be linked to this gene. Er3 gene was located in pea LGIV at 0.39 cM downstream of marker AD61. The location of Er3 gene in the pea map is a first step toward the identification of this gene.

A comparison of organic fungicides: alternatives for reducing scab on pecan

In the southeastern USA, the most widespread and damaging disease of pecan is scab, caused by Venturia effusa. Although scab can be controlled using conventional chemical methods, organic pecans that attract a premium price mandate the use of organic fungicides. Also, organic production is an environmentally sustainable method. However, where susceptible pecan cultivars are grown, there are limited options for organic management of scab. We conducted experiments to compare organic fungicides to control scab on the susceptible cv. Desirable in 2011, 2012, 2014, 2015, and 2016. The alternatives compared included Bordeaux mixture, compost tea, sodium bicarbonate, Bacillus subtilis, sulfur, cuprous oxide, and extract of the Giant Knotweed (Reynoutria sachalinensis). Rainfall and scab severity differed between seasons. There was consistently low severity on foliage, with little or no difference between treatments. Similarly at the time of the first fruit assessment, the severity was low and the differences in severity small and inconsistent between seasons and treatments. However, by the time of the second fruit assessment, severity of scab had increased and consistent differences among treatments existed (except in the drought year of 2011, when scab severities were very low and similar to the control). In all other years, the control treatment had significantly more severe scab compared to some (2012 and 2014) or all other treatments (2015 and 2016). Extract of the Giant Knotweed as a fungicide was included in 2012, 2014, 2015, and 2016, and fruit on those trees had less severe scab in all years compared to that on fruit of the control trees. In three seasons (2012, 2015, and 2016), applications of Bordeaux mixture resulted in a reduction in scab severity. Compost tea, Sodium bicarbonate, B. subtilis, sulfur, and cuprous oxide significantly reduced scab compared to the control in one or two seasons, but were not consistent among seasons, and were never more efficacious compared to the extract of the Giant Knotweed. Extract of the Giant Knotweed and Bordeaux mixture appear to offer the greatest potential as organic approaches for managing scab in pecan. However, wherever possible, planting of scab resistant cultivars should be considered as a first line of defense.

Changes in lignin biosynthesis and monomer composition in response to benzothiadiazole and root-knot nematode Meloidogyne incognita infection in tomato

Benzothiadiazole (BTH) acts as a priming agent in plant defence leading to a reduction in penetration and development of the root-knot nematode Meloidogyne incognita in susceptible tomato roots. Changes in lignin biosynthesis in the susceptible tomato cv. Roma following nematode infection and/or BTH treatment were investigated in comparison to the resistant cv. Rossol. Both untreated and BTH-treated susceptible infected roots (galls) showed an increased level of expression of lignin synthesis-related genes (PAL, C4H, HCT and F5H) at early times during infection (2–4 days post inoculation). Peroxidase (soluble and cell-wall bound, POX) enzyme activities increased after inoculation with M. incognita and the priming effect of BTH treatment was evident at later stages of infection (7 days post inoculation). As expected, the induction of PAL and POXs and lignin synthesis-related genes was faster and greater in resistant roots after infection. Histochemical analysis revealed accumulation of higher lignin levels at later infection stages in BTH-treated galls compared to untreated ones. Furthermore, the monomer composition of lignin indicated a different composition in guaiacyl (G) and syringyl (S) units in BTH-treated galls compared to untreated galls. The increase in G units made G/S ratio similar to that in the resistant genotype. Overall, lignin played a critical role in tomato defence to M. incognita in response to BTH.

Nematicidal effect of Lepidium sativum on activity and reproduction of potato cyst nematode Globodera rostochiensis in soil

In Iran, potato cyst nematode (Globodera rostochiensis) jeopardizes the traditionally high yields of potatoes in Hamadan Province in the west of Iran. Biofumigation is an eco-friendly method for integrated management of plant parasitic nematodes. In the laboratory, water extracts of water cress, fenugreek and dill similarly reduced viability of second stage juveniles after 3 h of exposure, and decreased hatching of encysted eggs to less than 1%. Pre-treatment and combined tests similarly decreased hatch. The nematicidal efficiency of top green manure of Lepidium sativum on the survival of nematode was tested on a susceptible cv in microplots. The weights of biofumigated plants increased. Anti-hatching properties of water cress applied as a biofumigant reduced hatch by average of 56%. Reproduction rates were lowered to below one, and final populations of cysts and their egg contents were reduced by nearly 60% in treated soil. Biofumigation at a 1% amendment rate was sufficient to bring about these results, which were comparable with those achieved with 2 and 3% rates. Nematicidal isothiocyanates released after incorporating glucosinolate-containing brassica plants are fully biodegradable and less toxic than their synthetic equivalents, and their use is considered a safer alternative to soil fumigants such as methyl bromide.

The Foc gene governs resistance to race 3 of Fusarium oxysporum f. sp. cucumerinum in the cucumber cv. SMR-18

The genetics of resistance to race 3 of Fusarium oxysporum f. sp. cucumerinum (FOC race 3) in the cucumber cv. SMR-18 (P1) was investigated by crossing it with the susceptible cucumber cv. Ashley (P2) and evaluating the disease reaction in the parents, F1, F1 reciprocal, F2 and backcross (BC1P1 and BC1P2) populations. Resistance of cv. SMR-18 to FOC race 3 was consistent with that of a single dominant, nuclear gene. To study the linkage relationship between this gene and the Foc gene, which expresses resistance to both FOC races 1 and 2, 73 plants that were backcrossed to the susceptible parent (BC1P2) were self-crossed. Each resulting F2 family was evaluated for resistance or susceptibility to race 1 and race 3 by inoculating different groups of 15–20 plants with each race of the pathogen. Segregation data exhibited an absolute linkage between the Foc gene and the gene controlling resistance to race 3 of the pathogen, since no recombinants were observed and only the two parental classes at a frequency of 50% each were observed. Our data support the concept that the Foc gene, which controls resistance to races 1 and 2, also confers resistance to race 3.

Cell wall features transferred from common into durum wheat to improve Fusarium Head Blight resistance

Durum wheat is naturally more susceptible to Fusarium graminerum infection in comparison to common wheat. The improvement of durum wheat resistance against F. graminearum is a challenge due to the lack of resistance sources in its gene pool. FHB-resistance factors were introduced in durum wheat by generating recombinant inbred lines (RILs), obtained by crossing the hexaploid resistant accession 02-5B-318 with the susceptible durum wheat cv. Saragolla. In this work we explored the possible contribution of cell wall (CW) in RILs with improved FHB resistance. We thoroughly studied CW components, mycotoxins content and the expression of related genes in different RILs selected for their extremely high and low resistance to FHB. Differences were found in resistant and susceptible lines in the degree of pectin methylesterification and in deoxynivalenol (DON) accumulation after fungal infection. Genes involved in biochemical modification of CW structure (WheatPme-1, Glu-1) and mycotoxins accumulation (ns-LTP-1) were analyzed as putative candidates for FHB resistance. Our results indicate that durum wheat plants with cell wall structure and gene response acquired from common wheat displayed an increased resistance to FHB.

A new interspecific pear cultivar Yutaka: highly resistant to the two major diseases scab and black spot on Asian pears

Scab, caused by Venturia nashicola, is the most important disease of Asian pears. In Japan, the most popular and widely grown pear cultivar (cv.) Kousui is resistant to black spot, caused by the Japanese pear pathotype of Alternaria alternata, but highly susceptible to scab. Recently, a new interspecific pear cv. Yutaka carrying high fruit quality was registered officially after a cross between the Chinese pear cv. Hongli and the Japanese pear cv. Housui. Accordingly, tests were conducted to assess resistance of cv. Yutaka to scab, black spot and anthracnose. When conidial suspensions of V. nashicola were spray inoculated onto potted trees, leaves of cv. Yutaka showed no disease symptoms although severe scab development was recorded on the susceptible reference cv. Kousui. Furthermore, neither black spot symptoms nor necrosis formation were observed when leaves of cv. Yutaka were inoculated with conidial suspensions of the A. alternata Japanese pear pathotype or treated with a culture filtrate containing the host-specific AK-toxin of this pathogen, respectively. These results strongly indicate that cv. Yutaka is highly resistant to scab and black spot. Inoculation tests also suggested the potential high levels of resistance of cv. Yutaka to anthracnose caused by Colletotrichum gloeosporioides sensu lato. The introduction of this new pear cultivar will reduce fungicide applications in pear orchards and thus lower the risk of fungicide resistance development in these pathogens.