Susceptible Cvs Research Articles

First report of fig tree dieback caused by Lasiodiplodia theobromae in Tunisia

AbstractIn Tunisia, common fig (Ficus carica L., Moraceae) is a very ancient fruit crop, very important and still regaining interest. It is cultivated throughout Tunisia from the south to the north and from the east to the west. In July 2020, a severe unusual branch dieback and stem canker was observed on fig cv. ‘Zidi’ trees in a commercial orchard in north‐eastern Tunisia. Disease incidence was 50% and symptoms observed on the 10‐year‐old infected trees included wilt, defoliation, branch dieback and trunk and shoot cankers. The current study aimed to characterize the pathogen (s) associated with observed fig dieback and to study their pathogenicity. The causal agent has been identified as belonging only to the species Lasiodiplodia theobromae based on morphological characters and phylogenetic analyses, using combined sequences of ITS, tef1 and β‐tubulin (tub2) genes. Pathogenicity tests performed on 1‐year‐old detached and green shoots demonstrated that L. theobromae was pathogenic to common fig cv. ‘Zidi’. Symptom development was visible after 7–15 days of incubation at 25°C showing the aggressive behaviour of L. theobromae towards fig shoots. Cvs. ‘Chetoui’, ‘Zidi’, ‘Bidhi Bghal’ and ‘Bither Abyadh’ were less susceptible compared to the more susceptible cvs. ‘Soltani’ and ‘Bidhi 2’. To our knowledge, this study is the first report on common fig canker and dieback disease caused by L. theobromae in Tunisia and Africa. Considering the severe and rapid progress of this disease, prevention and management strategies should be implemented urgently to reduce its incidence and reduce fig tree losses.

Physiological and histological aspects of innate and shiitake-induced resistance against bacterial spot on tomatoes

This study aimed to evaluate the protective effects conferred by polysaccharides obtained from basidiocarps discarded from the commercial production of Lentinula edodes (shiitake mushroom) in tomato cultivars against bacterial spot disease and to study their mode of action. Among 13 cultivars analyzed for resistance to Xanthomonas gardneri cvs. Kada, Natalia and Sena were selected and sprayed with polysaccharides from shiitake (PSHII – 1.5 mg/mL) or distilled water 4 days before inoculation with the bacteria. PSHII promoted a 37.7% reduction in disease severity and its mode of action on plants was evaluated according to changes in photosynthetic parameters, and histopathological aspects. Leaves of plants treated with PSHII showed lower stomatal conductance and transpiration rate compared to the control, at the time of inoculation. In addition, in plants of the most susceptible cvs. (Kada and Natalia) treated with PSHII, phenols accumulated in cells close to the epidermis. We observed that the plants of the most resistant cultivar, Sena, presented higher stomatal density, mesophyll thickness and size of palisade cells. In Sena, we also observed intense cell proliferation near the X. gardneri infection site and deposition of phenolic compounds inside the mesophyll. Control of bacterial spot in different tomato cultivars through induced resistance and the mechanisms presented by the plants to resist the bacteriosis are discussed.

Bacterial and Fungal Pathogen Synergetics after Co-infection in the Wheat (Triticum aestivum L.)

Wheat is one of the most important staple grains in the world and the leading source of calories, production is limited by biotic stress. There is a number of pathogen attacks on wheat crops, depending on environmental conditions. In some cases, more than one crop pathogen attack leads to higher damage or decrease susceptibility. There are very few studies in the field of multiple pathogen interactions; in this study, we analyzed the co-infectionof wheat with fungal and bacterial pathogens. Field isolated Xanthomonas translucens and Xanthomonas compestris bacteria have been used against GM-322 and PDKV varieties co-infected with Fusarium fungus spp. In our experiment, we used Fusarium oxysporum, Fusarium graminearum, Fusarium equitus. Compared to the combined effect of the fungus and bacteria, we measured the length and width of the infected leaf part. We have observed that there is more susceptibility to X. compestris and F. graminearium in the GM-322 wheat variety. The second susceptible cvs was PDKV when we co-infected F. oxysporum and then X. translucens fungal and bacterial infected symptom analysis showed yellow stripes on the leaf surface of the wheat crop. We observed head blight in wheat when it was infected with F. graminearum and X. compestris. As a result, we concluded that varietal susceptibility also depends on co-infection pathogen attacks and their synergetic interaction.

Genesis of ultra-specialized histology with stable traits in mesophyll of drought tolerant apple cultivars

Even if some biological defense responses are activated instantaneously after stress occurrence, but other mechanisms of drought tolerance could be probed, detected and diagnosed as sable traits at mesophyll level. The present observations demonstrated multilateral modifications in different leaf parts, specialized parenchyma tissues and cribro-vascular bundles that facilitate vital activities in tolerant apple cultivars. In 2006, long deficit irrigation occurred in commercial apple collection containing 93 cultivars located in Karaj-Iran. Entire bearing 16-Year-old trees lost completely the crop except 16 CVs which were assessed for yield per tree since June drop to physiological maturity. Based on thehypothesis, stable traits were developed against drought stress through phenomenon of genesis. 19 different anatomical traits of mesophyll were accurately assessed in the selected resistant CVs compared with the susceptible "Golden Delicious" and native "Assali" as the controls. Microscopic studies computed on the transversal sections of mesophyll prepared by microtome ascertained ultra-specialized histological traits in the selected CVs. Morphologically, basal part of the main vein was completely spherical, outfitted, highly ordered and tidy tissues. Epidermis underlying layer was composed of well-organized tissues containing uniform cells by shape and size, inserted consistently next to one another in neat order with no intercellular space. Contrarily, controls showed opposite rhythm in all examined characters. Also, the mean number of epidermis layers at leaf margin resulted higher related to susceptible CVs. The mean number of vascular bundles and stomata decreased in tolerant CVs. These observations put in evidence some stable ultra-specialized histological traits of mesophyll, as a result of genesis route.

Role of salicylic acid in systemic resistance induced by Pseudomonas fluorescens and Trichoderma harzianum against Alternria solani in tomato

Tomato growers are suffering all over the world from massive losses due to root rot diseases, the study aims mainly to study the effect of treatment with many safe fungal and bacterial biological control agents as indicative signal particles to induce host systemic resistance under greenhouse conditions. Some essential parameters and evidences of resistance were determined, i.e. accumulation of salicylic acid (SA).One week after inoculation tomato seedlings with A. solani, previously pretreated with the tested biological inducers, endogenous SA content showed significant increase in all the tested cultivars. Moreover, SA content in resistant cvs were higher, compared with susceptible cvs (1.04-fold over that of susceptible CV).

고추약한모틀바이러스 병원형에 대한 파프리카 품종의 저항성 스크리닝

파프리카에 고추약한모틀바이러스가 감염되면 과일에 검은 반점이 형성되어서 상품과를 생산할 수 없다. 파프리카 10품종을 대상으로 PMMoV 병원형 <TEX>$P_{1.2}$</TEX> 및 <TEX>$P_{1.2.3}$</TEX>에 대한 저항성 품종 선발을 목적으로 생물 검정과 유전자 마커를 이용하여 분석하였다. 이들 품종에서는 Tobamovirus에 대한 저항성 저항성 마커형 <TEX>$L^1$</TEX>, <TEX>$L^3$</TEX> 및 <TEX>$L^4$</TEX>가 존재가 확인되었으나, <TEX>$L^2$</TEX> 저항성 마커형은 검출되지 않았다. SCAR와 CAPS 마커를 이용한 파프리카 품종의 저항성 마커형을 분석한 결과, 'Magnipico'와 'Easy'는 <TEX>$L^4L^4$</TEX>, 'Scirocco'와 'Orange glory F1'는 <TEX>$L^4L^3$</TEX>, 'Special F1'는 <TEX>$L^4L^1$</TEX>, 'Fiesta', 'Piero' 및 'Derby'는 <TEX>$L^3L^3$</TEX>, 'Cupra'와 'Mazzona F1'는 <TEX>$L^3L^1$</TEX>이 확인되었다. 2종의 병원형에 대한 저항성 품종은 'Magnipico', 'Easy', 'Scirocco F1', 'Orange glory' 및 'Special F1'이었고, 감수성 품종은 'Fiesta', 'Piero', 'Derby', 'Cupra' 및 'Mazzona F1'이었다. <TEX>$L^4$</TEX>의 유전형이 부재한 이들 감수성 품종은 PMMoV-<TEX>$P_{1.2.3}$</TEX>을 접종시 전신 감염되었다. 하지만 이들 품종은 저항성 마커형 <TEX>$L^3$</TEX>가 존재함에도 불구하고 PMMoV-<TEX>$P_{1.2}$</TEX>를 접종시 접종엽은 엽맥을 따라 괴사가 일어나면서 식물체의 상단부위는 과민감한 괴사 증상이 나타났다. The Paprika plant infected with Pepper mild mottle virus (PMMoV) do not produce commercial fruit as causing necrotic spots symptom on the fruit. Ten cultivars of paprika were analyzed to select the resistance cultivars against PMMoV pathotypes, <TEX>$P_{1.2}$</TEX> and <TEX>$P_{1.2.3}$</TEX>, using bioassay and genetic markers. <TEX>$L^1$</TEX>, <TEX>$L^3$</TEX>, and <TEX>$L^4$</TEX> genotypes expressing resistance to the pathotypes existed in those cultivars but <TEX>$L^2$</TEX> genotype did not. <TEX>$L^4L^4$</TEX> in cvs. Easy and Magnifico, <TEX>$L^4L^3$</TEX> in cvs. Scirocco and Orange glory F1, <TEX>$L^4L^1$</TEX> in cv. Special F1, <TEX>$L^3L^3$</TEX> in cvs. Fiesta, Piero and Derby, and <TEX>$L^3L^1$</TEX> in Cupra and Mazzona F1 were identified with SCAR and CAPS markers. The resistant cvs. to the 2 pathotypes were Magnipico, Easy, Scirocco F1, Orange glory and Special F1 and the susceptible cvs. were Fiesta, Piero, Derby, Cupra and Mazzona F1. The susceptible cvs. of the absence of <TEX>$L^4$</TEX> genotype showed systemic infection when inoculated with PMMoV-<TEX>$P_{1.2.3}$</TEX>. However, those cvs. despite the presence of <TEX>$L^3$</TEX> genotype showed vein necrosis on the inoculated leaf and hypersensitive necrosis symptom on the upper parts when inoculated with PMMoV-<TEX>$P_{1.2}$</TEX>.

Impact of the Mediterranean fruit fly (Medfly) Ceratitis capitata on different peach cultivars: The possible role of peach volatile compounds

The relationship between susceptibility of different peach cultivars (cvs) to the Mediterranean fruit fly (medfly), Ceratitis capitata, and the volatile composition of ripe fruit of each cv has been investigated, since understanding the fruit-insect interaction mechanism is crucial for developing control strategies for such a pest. Volatile compounds were analyzed by SPME–GC–MS in three cvs highly susceptible to medfly attack (Fair Time, Flaminia, Sicilia Piatta), and in two less susceptible cvs (Percoca Romagnola 7 and Doctor Davis). Among the volatile compounds detected, 88 could be identified. The main differences found in the volatile composition of the cvs, concerned the relative abundance of esters. The least susceptible cvs, above all Percoca Romagnola 7, contained the higher amounts of hexenyl, hexyl, 3-methylbutyl, butyl and 2-methylpropyl esters; among these, some C6 derivatives detected, such as (Z)-3-hexenyl acetate, are known to act as priming agents, enhancing plant defence response to insects. Instead, a lower relative content of methyl esters, such as methyl hexanoate and methyl octanoate, known to act as medfly pheromone and attractant respectively, was found in the least susceptible cvs.

Marker analysis for detection of the Mi-1.2 resistance gene in tomato hybrid rootstocks and cultivars

In tomato, the REX-1 marker is typically used to detect the root-knot nematode resistance gene Mi-1.2 in Solanum lycopersicum cultivars with introgression from S. peruvianum (Sp). However, using this marker, false positives have been reported in hybrid tomato rootstocks with introgressions from other Solanum species. We evaluated the reliability of available PCR-based markers Mi23, PMi and PM3 for detection of root-knot nematode resistance in a set of tomato hybrid rootstocks, cultivars and in several accessions of different Solanum species. Results showed that none of the tested markers was able to identify unequivocally lines with resistant phenotype. The Mi23 marker amplified from the susceptible tomato cvs Ailsa Craig and Chatham was Sp-like, while the PMi marker was highly polymorphic in several accessions of Solanum species and did not distinguish between a susceptible accession of S. peruvianum (LA1336) and two resistant accessions/clones (PI270435-2R2 and PI270435-3MH). In addition, the PM3 marker generated amplification products from the susceptible tomato cv. Tyrmes and susceptible accessions of S. chilense (LA1969 and LA2746) that were also Sp-like. Fingerprinting Mi-1.2 gene homologues (MiGHs) using primers flanking intron-1 in the tomato hybrid rootstocks and nematode-resistant and susceptible cvs indicated a great variation in the number and nature of the MiGHs. In silico analysis with the existing Mi-1.2 gene-specific primers C1/2, IMO-F1/R1 and VIGS-F indicated that they were not specific for the Mi-1.2 gene as they could amplify a fragment with a similar size from MiGHs from S. lycopersicum as well as other MiGHs from S. peruvianum. A newly designed Mi-1.2 gene-specific primer, Pau-do, used with an existing primer, C2S4, amplified an identical fragment of 1494 bp from cDNA of nematode-resistant tomato cv. Motelle and rootstocks Beaufort and Maxifort. Overall, this paper provides information to breeders, scientists and growers on the limited reliability of the available molecular tools to characterise root-knot nematode resistance in hybrid tomato rootstocks. The results show that, as most of the current markers are not universal and can lead to the appearance of false positives for root-knot nematode resistance, the resistance response of hybrid tomato rootstocks will still need to be evaluated through infection tests.

Aphid resistance in raspberry and feeding behaviour of Amphorophora idaei

The raspberry aphid Amphorophora idaei is a major pest of the raspberry plant and a vector of different viruses like Raspberry leaf mottle virus (RLMV), Raspberry leaf spot virus (RLSV), Black raspberry necrosis virus (BRNV) and Rubus yellow net virus (RYNV). Aphid resistant raspberry genotypes additionally show a reduced occurrence of viruses, thus the aim of this study was to investigate whether the feeding behaviour of A. idaei differs between aphid resistant and susceptible plants. In a biotest the cultivars (cvs.)‘Titan’,‘Rumiloba’,‘Nootka’,‘Schoenemann’,‘Williamette’ and‘Autumn Bliss’ show different levels of resistance. A significantly lower population was observed after 27 d on the resistant cvs.‘Rumiloba’ and‘Autumn Bliss’ in comparison to the other cultivars tested. The number of aphids on cv.‘Nootka’ was higher than on the resistant cultivars but significantly lower than on the susceptible cvs.‘Titan’,‘Williamette’ and‘Schoenemann’. The feeding behaviour was studied over a period of 12 h on plants of the cvs.‘Rumiloba’,‘Nootka’,‘Schoenemann’ and‘Autumn Bliss’ by using the electrical penetration graph (EPG) technique. Overall between 62% and 68% aphids tested per cultivar made probes on the leaves and penetrated into the phloem. On the resistant cv.‘Rumiloba’ the aphids started to probe considerably later (49.3 min) than on the other cultivars (12.1 to 33.1 min). In contrast, the first probe on‘Rumiloba’ was shorter (2.2 min) than on the resistant cultivars (23.9 to 63.5 min). On average the aphids attained the phloem on the susceptible cv.‘Schoenemann’ considerably earlier (221.1 min) than on the resistant cultivars (349.5 to 370.4 min). On the resistant cv.‘Nootka’ significant differences were found for the duration of phloem salivation (E1-pattern, 810.9 s in comparison to 24.3 to 176.9 s), the number of phloem salivation phases (2.7 in comparison to 0.1 to 0.2) and the number of phloem contacts before the sustainable phloem feeding (> 10 min) started (1.1 in comparison to 0.1 to 0.2). No differences were found between the cultivars for the number and duration of potential drops (cell penetrations) during the pathway to the phloem, analysed during the first 2 hours of the experiments. The obtained results indicate that the probing and feeding behaviour of A. idaei, which is responsible for virus transmission, is not sufficiently different between resistant and susceptible cultivars to be the reason for virus resistance.

Relationship between the Occurrence of Internal Browning and Size of Xylem Parenchymatous Cells in Roots of Japanese Radish

The correlation between the occurrence of internal browning (IB) and the size of root xylem parenchymatous cells in Japanese radish (Raphanus sativus L.) was determined in 3 experiments. The first examined intervarietal differences in IB among 5 commercial cultivars (cvs.). Results revealed that the differences in susceptibility to IB largely depend on root cell size, and that mean cell length in IB-resistant cvs. was approximately 39–45% shorter than in susceptible cvs. The second experiment examined the relationship between cell size and IB occurrence in 3 IB-susceptible commercial cvs. and their ‘Gensuke’ F1 hybrids. In every F1 hybrid strain, the central region did not appear to show the propensity of its parents to develop IB, and mean cell length in the former was approximately 26–39% shorter than in the latter. The third experiment examined the effect of applying a plant growth regulator on IB occurrence and cell size. Gibberellin (GA) application during the mid-growth stage restricted IB occurrence, and the mean cell length of GA-treated plants during this period was approximately 27–47% shorter than in the control. These results strongly suggest that IB occurrence is largely dependent on the size of root xylem parenchymatous cells, and IB seldom occurs in roots with smaller cells.

APHID TOLERANCE OF DIFFERENT HOP GENOTYPES: FIRST ATTEMPTS TO DEVELOP A SIMPLE BIOTEST FOR HOP BREEDING BY THE USE OF PHORODON HUMULI

A keystone of future pest management in hops is the breeding of cultivars (cvs.) that are tolerant or resistant to Phorodon humuli infestation. During 2006 and 2007 first attempts were made for the development of a biotest concerning the aphid susceptibility of different hop genotypes. We chose for these tests the susceptible cvs. 'Hallertauer Magnum' (HM) and 'Herkules' (HS), the aphid-tolerant or -resistant cvs. 'Spalter Select' (SE) and 'Boadicea' (BO), and two apparently resistant genotypes from our germplasm - the male accession 38 and the wild hop Jena 49. Aphid cages were mounted to leaves taken from potted greenhouse plants of these six genotypes, and each cage was equipped with an aphid larva with known day of birth. The leaves (12 replications per genotype) were stored in a climate chamber, and the 72 cages opened three times a week to count and remove all newborn larvae. The mother aphids stayed in their cages until the death of the last aphid marked the end of a series. Altogether eight series were conducted. The cumulative alive offspring of one aphid was highest on HM, with an overall mean number of 66.2 larvae, and lowest on 38, with 14.9 larvae. However, overall means of the other cvs. were not significantly lower - 59.7 on HS, 59.6 on SE and 57.6 on BO. The maximum number of larvae produced by one aphid was 115 on HM. The lifespan of the aphids was longest on HM, with an overall mean of 39.8 days, and shortest on 38, with 24.4 days. The other genotypes produced similar lifespans from 31.7 to 34.3 days. The record holder survived on HM for 69 days. These results, especially concerning the aphid-tolerant cvs. BO and SE, demonstrate that for the development of a practical, simple aphid biotest there is still a long way to go.

DURABLE RESISTANCE OF APRICOT CULTIVARS HARLAYNE AND BETINKA TO SIX DIFFERENT STRAINS OF PLUM POX VIRUS

Results of a six-year evaluation carried out in the Czech Republic (CR) for resistance of apricot cvs Harlayne and Betinka to six different strains and isolates of PPV are presented. Two-year-old trees of both cultivars were inoculated by chip budding with PPV-M (type strain), PPV-D (type strain), PPV-Rec (originally recovered in the CR as PPV-W), PPV-M (isolated in the CR from peach), PPV-D (isolated in the CR from Prunus insititia), and PPV-Rec (isolated in the CR from P. insititia). PPV susceptible apricot cvs Karola and Velkopavlovicka were used as controls and were chip-bud inoculated with PPV strains. No symptoms appeared in the leaves and fruits of cv. Betinka during six years of observation following inoculation with PPV-D (type), PPV-D (P. insititia), PPV-Rec (PPV-W), PPV-M (peach) and PPVRec strains, and in two trees inoculated with PPV-M (type) strain. Likewise, ELISA did not detect the presence of PPV in the leaves of both cultivars. RT-PCR gave a slight positive reaction from the leaves of a symptomless tree of cv. Harlayne inoculated with PPV-Rec (PPV-W) and from leaves of a symptomless tree of cv. Betinka inoculated with PPV-D (P. insititia). The presence of PPV in these trees is under investigation. Mild diffuse rings and spots appeared occasionally in the leaves and fruits of one tree of cv. Betinka after inoculation of PPV-M (type). The presence of PPV was confirmed by ELISA and RT-PCR. The relative concentration of PPV-M (type) protein in the leaves of a tree of cv. Betinka determined by ELISA was low (2.5×10-1) in comparison with the control (cv. Karola, 1.95×10-3). Severe symptoms appeared in the leaves and fruits of susceptible control cvs Karola and Velkopavlovicka. The presence of different PPV strains in control cultivars was confirmed by ELISA and RTPCR. Thus, cvs Harlayne and Betinka displayed durable resistance to the six different strains and isolates of PPV over the six year trial.

Susceptibility of eight potato cultivars to tuber infection by Phytophthora erythroseptica and Pythium ultimum and its relationship to mefenoxam‐mediated control of pink rot and leak

AbstractIn addition to cultural practices, the application of the fungicide mefenoxam is an important disease management tactic used to control both pink rot and leak on potato tubers grown in the USA. Mefenoxam resistance has been identified in many of the potato growing regions, and therefore resistance management strategies are very important for retaining this fungicide as a tool to manage these storage rot diseases. The relationship between mefenoxam efficacy and cultivar susceptibility to pink rot and leak was assessed in post‐harvest inoculation studies. Mefenoxam was applied to potato (Solanum tuberosum) cultivars known to express varying levels of susceptibility to pink rot and leak caused by Phytophthora erythroseptica and Pythium ultimum, respectfully. Tubers harvested from plants treated with in‐furrow and foliar applications of mefenoxam were inoculated with isolates sensitive to the fungicide. Incidence and severity of both diseases ranged widely among cultivars. Russet Norkotah was the most susceptible to infection by P. erythroseptica, while cvs Pike and Atlantic were the most resistant. Cultivars Dark Red Norland, Russet Norkotah, Goldrush and Russet Burbank were most susceptible to infection by P. ultimum whereas Snowden was most resistant. Control of pink rot differed significantly among cultivars following mefenoxam treatment, ranging from 28% (cv. Goldrush) to 67% (cv. Snowden) and generally provided the greatest level of disease control on susceptible and moderately susceptible cultivars such as Russet Norkotah and Snowden, respectively. In contrast, the impact of mefenoxam on leak development was minimal and disease control did not differ significantly among the cultivars. The fungicide failed to control leak in the susceptible cvs Atlantic and Pike and control ranged from 1.7% to 5.2% in cvs Goldrush, Russet Norkotah, Dark Red Norland, Russet Burbank and Kennebec. The greatest level of leak control was achieved with the moderately resistant cv., Snowden, at 12.7%. Cultivars most likely to benefit from mefenoxam treatments should be targeted as part of a pink rot management programme. Judicious use of the fungicide, when matched with the level of cultivar susceptibility, may prove to be an efficient and effective approach to reduce infection rates and possibly manage mefenoxam resistance thereby maintaining longevity of the compound.

Determination of agronomic practices for the management of blight of chickpea caused by Ascochyta rabiei in Turkey: 1. Appropriate sowing date

In order to determine the most appropriate dates for planting chickpea in central Anatolia, Turkey, six cultivars were planted at three sites that differed in disease pressure. In two of the sites, disease pressure from Ascochyta rabiei was promoted by spreading infected chickpea debris on the soil surface at the time of planting and, at one of these, sprinkle irrigation was applied. In the third site, where conditions were dryer, no artificial inoculum was provided. Plants from seeds sown in early March had the most disease and in the sprinkle irrigated plots the disease severity ranged from 7.8 on the most susceptible cv. Canitez to 3.3 on the least susceptible Gokce as scored on the 1–9 scale where 1 = no disease and 9 represents a plant killed by the fungus. There was an inverse relationship between disease severity and yield, production from blight resistant cultivars of around 2,000 kg ha−1 being more than twice that of susceptible ones. Delaying planting for 3–5 weeks reduced the severity of ascochyta blight but also reduced the yields in four of the six cultivars. In contrast, reduction in disease severity by delayed sowing resulted in yield increases for the susceptible cvs Canitez and Local, although yield level was not as much as those of the less susceptible cvs sown early. Delay of 6–9 weeks almost eliminated ascochyta blight but yields of all cultivars were seriously compromised by drought stress. In consequence, chickpea farmers are recommended to use resistant or tolerant cultivars and sow early in March. For less resistant cultivars, sowing in early April is recommended. Further delay is not recommended unless irrigation is provided and fungicide spraying is recommended where signs of infection are present under conditions conducive to the disease.

Microscopic and Macroscopic Studies of the Development of Puccinia hemerocallidis in Resistant and Susceptible Daylily Cultivars.

Infection and colonization of eight daylily cultivars, which varied in resistance to daylily rust, by Puccinia hemerocallidis was studied macroscopically and microscopically. After germination of urediniospores, appressoria formed at the tip of germ tubes and the fungus penetrated the host through stomatal openings 2 days after inoculation (DAI). Under the infection sites, intercellular hyphae aggregated and formed uredia, which released urediniospores 8 DAI. Resistant cultivars, characterized by the development of rapid death of host cells, were separated into three qualitative categories based on absence and presence of necrotic lesions without or with sporulation. In highly resistant cvs. Prairie Blue Eyes and Bertie Ferris, no macroscopic disease symptoms were observed on leaf surfaces although a few collapsed cells were detected microscopically. Both resistant and moderately resistant reactions were characterized by necrotic lesions with many collapsed cells under infection sites. The difference between these two reactions was that uredia and urediniospores were observed in the moderately resistant cv. Chicago Apache, but not in resistant cvs. Buttered Popcorn and Stella De Oro. Susceptible cultivars, characterized by the absence of a hypersensitive response, were separated into two qualitative categories based on restriction of intercellular hyphal growth that delayed development of uredia and formation of urediniospores. Compared to the susceptible cv. Pardon Me, moderately susceptible cvs. Mary Todd and Chorus Line had a delayed latent period and reduced amount of sporulation. The results indicate that hypersensitive cell death is one of the resistance responses to daylily rust. Necrotic lesions on leaf surfaces are associated with the number of collapsed host cells. Delayed latent period and reduced sporulation that resulted from restriction of intercellular hyphal growth could represent another type of resistance response in the daylily-rust pathosystem.

Development of ascochyta blight (Ascochyta rabiei) in chickpea as affected by host resistance and plant age

Ascochyta blight caused by Ascochyta rabiei, is the most destructive disease in many chickpea growing countries. Disease development varies with the growth stage and host resistance. Hence, disease development was studied in cvs ICCX 810800 (resistant), ICCV 90201 (moderately resistant), C 235 (moderately susceptible), ICCV 96029 and Pb 7 (susceptible) under controlled environment (ICRISAT, Patencheru) and field conditions (Dhaulakuan, Himachal Pradesh) at seedling, post-seedling, vegetative, flowering and podding stages. Under controlled environment, the incubation period and terminal disease reaction (TDR) did not vary significantly at different growth stages against virulent isolate AB 4. Cultivars ICCX 810800, ICCV 90201 and C 235 showed a significantly longer incubation period than the susceptible cv. Pb 7. Cultivar ICCX 810800 showed slow disease progress and the least TDR. Field experiments were conducted during the 2003–2004 and 2004–2005 growing seasons. During 2003–2004, TDR was higher in plants inoculated at podding and the flowering stage and the lowest disease reaction was recorded in ICCX 810800. A severe epidemic during 2004–2005 was attributed to the favourable temperature, humidity and well distributed high rainfall. TDR did not differ significantly at any of the growth stages in susceptible cvs ICCV 96029 and Pb 7. With respect to seeding date and cultivar, the highest yield was recorded in the early-sown crop (1,276.7 kg ha−1) and in ICCV 90201 (1,799.3 kg ha−1), respectively. The yields were greatly reduced in all the cultivars during 2004–2005 and the highest yield was recorded in ICCX 810800 (524.7 kg ha−1). Integrated disease management using resistant cultivars, optimum sowing period and foliar application of fungicides will improve chickpea production. The experiment under controlled environment and field conditions (during the epidemic year) showed a similar disease development.

Characterization of Wheat-Triticale Lines Resistant to Powdery Mildew, Stem Rust, Stripe Rust, Wheat Curl Mite, and Limitation on Spread of WSMV.

High yield potential and the wide adaptability of wheat-rye T1BL·1RS translocation lines are attractive to breeders. The wheat-rye lines Lankao 1, 3, 4, and 5 were resistant to a wide spectrum of wheat powdery mildew (Blumeria graminis f. sp. tritici) isolates from both China and Canada. They also were resistant to a mixture of wheat stem rust (Puccinia graminis f. sp. tritici) pathotypes (98WSR) and wheat stripe rust (P. striiformis f. sp. tritici) races from western Canada and China. Colonization of wheat curl mite (WCM) (Aceria tosichella) resulted in slower development of rolling and trapping leaves in the Lankao lines than in the WCM-susceptible check cultivars. The delayed development of Wheat streak mosaic (WSM) symptoms on Lankao lines was observed when transmitted by viruliferous WCM, even though they were susceptible to Wheat streak mosaic virus (WSMV). This effect of Lankao lines on limiting the spread of WSM was comparable with other known sources of WCM resistance. Sequential C-banding and genomic in situ hybridization analyses revealed the presence of a pair of T1BL·1RS translocated chromosomes in the Lankao lines. Segregation analysis of the F2 progeny plants derived from crosses between Lankao 4 and the susceptible wheat cvs. Mingxian 169 and Lovrin 13 indicated that a single dominant gene was responsible for the isolate-specific resistance against wheat powdery mildew in Lankao 4. Polymerase chain reaction analysis using an STS marker amplified rye chromatin in powdery mildew-resistant and -susceptible F2 plants of the Mingxian 169 × Lankao 4 cross demonstrated that the resistance of Lankao 4 was not controlled by a gene or genes located on the rye chromosome arm of T1BL·1RS. The resistance of the Lankao lines to diseases and limitation of the spread of WSMV, in combination with good quality and high yield potential, makes them useful for wheat improvement and production.

Differences in the Development of Lateral Roots among Several Cultivars in Japanese Radishes (Raphanus sativus L.) under Low Temperature Condition

Seeds of cv. T-340 were sown in the field on 10 March and 9 April 1997. The lateral root (LR) production was progressively intensified in early sown plot (ESP) instead of late (LSP). Plants in the ESP produced roots with small mean weights, diameter and length as compared with those in the LSP. Early-sown seedlings were subjected to low soil temperature conditions, below approximately 12°C during the first growth stage. In a second experiment, seeds of cvs. T-340 and T-396 were sown in 2 experimental plots: a control plot and a high soil temperature plot (HTP). The minimum soil temperatures in the control were often remained below 10°C for about 25 days after sowing, but the temperatures in the HTP kept above 15°C during the growth period. When grown under the control, larger number of thickened LRs was observed in roots of cv. T-340, but roots of cv. T-396 did not exhibit this disorder at any soil temperature plot. In both cvs., hinder root elongation was observed in the control as compared with the HTP. In a third experiment, varietal difference in the occurrence of LR in roots of cvs. Oshin, T-340, T-396 and Tenpou was compared. Although no correlation was observed between the different cvs. and root growth, active meristematic activity was observed in the pericycle region outside the protoxylem in roots of susceptible cvs. Oshin and T-340. Conversely, this meristematic activity remained low in roots of resilient cvs. T-396 and Tenpou. These observations led to the hypothesis that the obstruction of root elongation caused by low soil temperatures (below 12°C) during the first growth period often results in activation of the basal region of the LR meristem in susceptible cvs. prompting LR development. However, in resilient cvs., the LR seldom occur, even when root elongation is inhibited by low soil temperatures that normally decrease the meristematic activity of this region.

Evaluation of leaf rust resistance genes Lr1, Lr9, Lr24, Lr47 and their introgression into common wheat cultivars by marker-assisted selection

Epidemiological field controls in different Italian locations and seedling evaluations of the ‘Thatcher’ near-isogenic lines (NILs) carrying the leaf rust resistance genes Lr1, Lr9, Lr24 and Lr47 were conducted during 5 years of testing. These genes confirmed their effectiveness in both field and greenhouse conditions. Moreover a backcross program was carried out by using as recurrent parents the susceptible high-quality common wheat cvs ‘Bolero’, ‘Colfiorito’, ‘Serio’ and ‘Spada’ and the ‘Thatcher’ NILs carrying the above mentioned genes as donor parents. The progenies of different cross combinations were selected by both resistance tests and marker assisted selection using molecular markers (STS, SCAR, CAPS) closely linked to Lr genes: a complete cosegregation was observed between the resistance genes used and the corresponding molecular markers.

Protection of Susceptible Potato Cultivars Against Late Blight in Mixtures Increases with Decreasing Disease Pressure

ABSTRACT Cultivar mixtures can reduce potato late blight severity on susceptible cultivars. While alternating rows of susceptible and resistant cultivars would be more acceptable than random mixtures for commercial use, they increase the genotype unit area, which is an unfavorable factor for mixture efficiency, and have been minimally efficient when disease pressure is high. The effects of disease pressure on the performance of alternating rows of cultivars possessing various types and levels of resistance were investigated in 2000 and 2001 near Quito, Ecuador, where natural pressure of late blight is high. The experiments included the highly susceptible cvs. Cecilia in 2000 and LBr37 in 2001, as well as C114 (moderately resistant) and PAN (highly resistant), planted as pure stands and as the three possible two-way combinations. Different disease pressures were obtained with three spraying schedules of a contact fungicide: nontreated, one spray every second week, and one spray weekly. The area under the disease progress curve (AUDPC) on the susceptible cultivar was 0 to 20% less in mixed than in pure plots when no fungicide was applied, 13 to 26% less with a biweekly application of fungicide, and 32 to 53% less with a weekly application. These values are comparable to those obtained in previous experiments in smaller plots with designs maximizing the distance between susceptible plants. No significant differences in mixture performance were observed according to the resistant cultivar included. Effects on yield were minimal, because of the impact of factors other than late blight. Disease pressure therefore appears as a major factor conditioning the efficiency of potato cultivar mixtures against late blight.