Development of Eyespot and Brown Foot Rot in Wheat Plants Inoculated with Mixtures of Pseudocercosporella herpotrichoides Types and Fusarium Species

The effects of Fusarium avenaceum, F. culmorum and Microdochium nivale on eyespot development and of types of the eyespot fungus Pseudocercosporella herpotrichoides on brown foot rot caused by the Fusarium or Microdochium spp. were investigated by sequential inoculation of wheat plants grown in pots in a controlled environment. The W-type of the eyespot fungus induced more severe disease than the R-type, but its symptons were suppressed to a greater extent by Fusarium spp., especially F. avenaceum. Brown foot rot symptoms were sometimes suppressed by P. herpotrichoides but were occasionally more severe when the Fusarium inoculum was applied after the P. herpotrichoides. There, sults are discussed in relation to observations of natural infections.     

Reactions of six cultivars of rice (Oryza sativa L.) to three fungal diseases

Abstract

Fungal diseases are the most important threat for rice production in the world. Rice fields were visited and sampled from diseased bushes to identify fungal diseases in Kohgiluyeh and Boyer-Ahmad province, in the south-west of Iran. Fungi were isolated from diseased tissues by Agar-plate method, and purified by single-spore or hyphal-tip methods. They were identified by studying morphological characteristics. The virulence of isolated fungi was evaluated on six dominant rice cultivars, Champa of temperate region, Champa of subtropical region, Gerdeh, Shamim, Fajr and Tarom, under greenhouse conditions. The experiment was set up in a factorial experiment in completely randomized design with four replicates. The incidence of three fungal diseases: brown spot caused by Curvularia australiensis and Bipolaris cookei, foot rot caused by Fusarium globosum and Fusarium sambucinum, and black root rot caused by Exserohilum pedicellatum, was proven in this study. Although, all of the tested cultivars significantly showed different reaction to these fungi, but the cultivars Champa of subtropical region and Tarom were resistant to foot rot as well as the black root rot and the cultivar Gerdeh was resistant to brown spot disease.     

Effects of cultivar and fungicides on stem-base pathogens, determined by quantitative PCR, and on diseases and yield of wheat

The polymerase chain reaction (PCR) was used to identify and quantify all fungal pathogens of wheat (Triticum aestivum) stem bases in nine field experiments at three locations in England. The main aim was to apply quantitative PCR to provide robust data on the efficacy of new fungicides against the individual components of the stem‐base disease complex. Cyprodinil most effectively controlled eyespot by decreasing both pathogens, Tapesia yallundae and T. acuformis (the most widespread species), and sometimes contributed to increased yields. Prochloraz controlled eyespot less consistently, its effectiveness dependent mainly on the presence of T. yallundae or on rainfall events soon after application. Azoxystrobin contributed to yield increases most consistently. Although it decreased sharp eyespot and its pathogen, Rhizoctonia cerealis, these effects were insufficient to account for much of the yield increases. The effects of fungicides on eyespot were sometimes greatest on the most susceptible cultivars. Amounts of Tapesia DNA were usually consistent with cultivar susceptibility ratings. The only pathogens of brown foot rot present in significant amounts were Microdochium nivale vars nivale and majus. They appeared not to affect yield or to respond greatly to fungicides. The susceptibility of cultivars to these pathogens was sometimes similar to their susceptibility to eyespot, suggesting that they may respond to the same host resistance genes or may in some cases be secondary colonisers of eyespot‐infected plants.     

First Report of <i>Fusarium striatum</i> Causing Root Rot Disease of <i>Panax notoginseng</i> in Yunnan,China

Panax notoginseng is a traditional Chinese medicinal plant. Root rot of P. notoginseng is one of the most serious diseases affecting P. notoginseng growth and causes wilted leaves, fewer lateral roots and rotten roots. Root rot is a soil-borne disease, and mainly occurs from June to August in Yunnan Province when the temperatures are high and the air is humid. In this study, the endophytic fungal genus Fusarium isolate E-2018.1.22-#3.2 was obtained from a P. notoginseng embryo. Fusarium isolate E-2018.1.22-#3.2 was identified as Fusarium striatum based on morphological characteristics and molecular analysis. The fungus was found to have conidiophores and macroconidia, and its ITS, LSU and TEF-1α genes shared 100%, 99.2% and 99% identities with the homologous genes of Fusarium striatum, respectively. Isolate F. striatum E-2018.1.22-#3.2 can cause root rot symptoms, including black, soft roots, fewer lateral roots and leaf wilt, in 93% of the experimental P. notoginseng plants, and could be re-isolated, fulfilling Koch’s postulates. When the P. notoginseng plants were treated with the fungicide pyraclostrobin, isolate F. striatum E-2018.1.22-#3.2 was unable to cause root rot. We have therefore demonstrated that F. striatum E-2018.1.22-#3.2 is able to cause root rot disease in P. notoginseng. This is the first report of root rot disease caused by F. striatum on P. notoginseng in China.     

Effects of soil fumigation on disease incidence, growth, and yield of spring wheat

Plots were fumigated with various amounts of D-D or 85% dazomet dust and sown with spring wheat given various amounts of nitrogenous fertilizer. Dazomet increased yield and decreased take-all disease in the first crop after application, but increased the disease in the second crop. Although D-D increased take-all slightly, it increased yield in 1966, but in 1967 it decreased yield and its use was associated with a severe ear deformity. Fumigation had little effect on eyespot, sharp eyespot, root browning (Fusarium spp.), or browning root rot (Pythium spp.), but decreased nematode damage where nematodes were numerous.     

Root Rot of Trifolium subterraneum Induced by Fusarium solani

A fungus disease of Trifolium subterraneum, previously unknown in South Africa, was identified as Fusarium root rot caused by F. solani (Mart.) Sacc. Diseased plants were severely stunted. The characteristic internal root discolouration observed in the field, is described. The disease occurred mainly between Swellendam and Humansdorp in the southern and south-eastern Cape Province. The subterranean clover fields inspected were between 95 and 100 % infected with the root rot disease. T. repens and T. pratense were also susceptible.     

Molecular characterisation of Fusarium oxysporum causing rot diseases in small cardamom (Elettaria cardamomum Maton)

Incidence of root rot and foliar yellowing, rhizome rot, panicle wilt and stem rot diseases of small cardamom (Elettaria cardamomum Maton) are caused by Fusarium oxysporum Schlecht., and were surveyed in the high ranges of Idukki district, Kerala during 2010–2011. The diseases were noticed in different areas to varying degrees. Root rot was found to be most severe, followed by pseudostem rot, rhizome rot and panicle wilt. The Fusarium infections were prevalent throughout the year (January–December) and varied from 1.5 to 10.6%. Even though the pathogen was isolated from different plant parts, during pathogenicity studies, all the isolates could cross-infect other plant parts too. Twenty different isolates of F. oxysporum were obtained from diseased samples, and five morphologically distinct isolates were analysed with Randomly Amplified Polymorphic DNA (RAPD) markers to study the genetic variability, if any, among them. PCR amplification of total genomic DNA with random oligonucleotide primers generated unique banding patterns, depending upon primers and isolates. Nine oligunucleotide primers were selected for the RAPD assays, which resulted in 221 bands for the five isolates of F. oxysporum. The number of bands obtained was entered into an NTSYS, and the results showed moderate genetic variability among F. oxysporum isolates causing root rot, rhizome rot, panicle wilt and pseudostem rot, collected from different locations. The dendrogram of different isolates into groups resulted in one major cluster at 0.61 similarity index comprising of four isolates (CRT 3, CRR 3, CPW 2 and CSR 1) and one isolate (CRT 5) formed in a separate cluster. Among the five isolates of F. oxysporum, CRT 5 was entirely different from the other four isolates. The isolates also differ according to the geographical area, as revealed from the genetic variability observed in different root rot isolates (CRT 3 and CRT 5). It is inferred that despite moderate variability, F. oxysporum, infecting small cardamom in Idukki district of Kerala, consists of a single clonal lineage.     

Effect of Leaf Infection by Kabatiella zeae on Stalk Rot Prevalence and Grain Yield of Maize Hybrids

Eight maize hybrids were tested for resistance to eyespot (Kabatiella zeae) and stalk rot (Fusarium spp.) under field conditions in 1993–1995. The relationship between eyespot and stalk rot and their effect on grain yield of hybrids were studied. Effectiveness of the prochloraz fungicide in controlling both diseases was evaluated. The experiments were performed in three subtrials where plants were naturally infected, inoculated with K. zeae or treated with the fungicide, Sportak 450 EC. The relationship between intensity of leaf damage by eyespot and incidence of stalk rot has been evidently confirmed. High infection of leaf by K. zeae reduced grain yield of hybrids. However, considerable differences in prevalence of disease and yield losses were noted in successive years. The intensity of eyespot depended upon environmental conditions highly variable over the years: it was enhanced by low temperature and high air humidity in July and August. Hybrids showed significant differences in susceptibility to both diseases. Mona – hybrid from the USA and two experimental hybrids from Poland were less affected by diseases than Smolimag and Hidosil (commercial hybrids from Poland). The fungicide Sportak was effective in controlling eyespot and had an indirect influence on decreasing fusarium stalk rot.     

Identity and Pathogenicity of Fungi Associated with Root and Crown Rot of Soft Red Winter Wheat Grown on the Upper Coastal Plain Land Resource Area of Mississippi

Seedling stand, disease severity and fungal incidence were determined from untreated ‘Wakefield’ soft red winter wheat planted on a Leeper silty clay loam in field tests conducted at the Mississippi Agricultural and Forestry Experiment Station, Plant Science Research Center, Mississippi State University, Starkville, Mississippi during the 1996–97 and 1997–98 growing seasons. Seedling stand was reduced by 40% each year in plots established with untreated seed. Cochliobolus sativus was the most frequently isolated fungus. Fusarium acuminatum, Fusarium equiseti and Fusarium solani were the most prevalent Fusarium spp. Seven other Fusarium spp. and 23 species of other fungal genera were isolated. Pathogenicity tests with three isolates each of C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, Fusarium compactum, Embellisia chlamydospora and Microdochium bolleyi were performed in test tube culture and two isolates each of C. sativus, C. spicifer, F. acuminatum, E. chlamydospora and M. bolleyi under greenhouse conditions. In test tubes and in the greenhouse, seedlings infected with isolates of C. sativus developed seedling blight, discoloration and necrosis, primarily in seminal roots and crowns. In the greenhouse, C. sativus induced lesions on the lower leaf sheath and reduced seedling height, seedling emergence, dry and fresh weight of roots and shoots. Isolates of F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora and M. bolleyi induced slight to moderate orange to light‐brown discoloration of crown and seminal roots in test tubes. Cochliobolus spicifer isolates had the most pre‐emergence activity, inducing black root discoloration and root pruning of wheat seedlings and reducing seedling emergence, root fresh weight and shoot dry weight. In the greenhouse, F. acuminatum reduced seedling height, seedling emergence and root and shoot dry weights. Microdochium bolleyi and E. chlamydospora reduced fresh and dry weight of roots, plant emergence and shoot dry weight. Fusarium acuminatum and C. spicifer reduced the growth rate of wheat seedlings. All fungi evaluated showed increased disease severity compared to the untreated control. The high frequency of isolation of C. sativus from crown and root tissues can be partially explained by the dry, warm conditions during the early stages of wheat seedling development in the Upper Coastal Plain Land Resource Area of Mississippi.     

Evaluation of Ochrobactrum anthropi TRS-2 and its talc based formulation for enhancement of growth of tea plants and management of brown root rot disease

Aim: To evaluate Ochrobactrum anthropi TRS‐2 isolated from tea rhizosphere and its talc based formulation for growth promotion and management of brown root rot disease of tea. Methods and Results: Ochrobactrum anthropi TRS‐2, isolated from tea rhizosphere could solubilize phosphate, produce siderophore and IAA in vitro and also exhibited antifungal activity against six test pathogens. Application of an aqueous suspension of O. anthropi to the rhizosphere of nursery grown tea seedlings of five varieties of tea (TV‐18, T‐17, HV‐39, S‐449, UP‐3 and) led to enhanced growth of the treated plants, as evidenced by increase in height, in the number of shoots and number of leaves per shoot. Treatment with O. anthropi also decreased brown root rot of tea, caused by Phellinus noxius. Multifold increase in activities of chitinase, β‐1,3‐glucanase, peroxidase and phenylalanine ammonia lyase in tea plants was observed on application of O. anthropi to soil followed by inoculation with P. noxius. A concomitant increase in accumulation of phenolics was also obtained. Further, talc based formulation of O. anthropi was prepared and its survival determined every month up to a period of 12 months. Ochrobactrum anthropi could survive in the formulation up to a period of 9 months with a concentration of 7·0 log₁₀ CFU g^?1, after which there was a decline. Talc formulation was as effective as aqueous suspensions in both plant growth promotion and disease suppression. Conclusion: Ochrobactrum anthropi, either in aqueous suspension or as talc formulation induced growth of tea plants and suppressed brown root rot disease. It induced defense responses in tea plants. Significance and Impact of the Study: Ochrobactrum anthropi and its talc based formulation can be considered as an addition to available plant growth promoting rhizobacteria (PGPR) currently being used for field application. The present study offers a scope of utilizing this bacterium for growth promotion and disease management which would help in reduction of the use of chemicals in tea plantations.     

Developmental Regulation of Susceptibility and Tolerance to Fusarium Root Rot in Beans

The soil-borne fungus, Fusarium solani f. sp. phaseoli, attacks roots and hypocotyls of bean (Phaseolus vulgaris) plants causing a devastating disease called root and foot rot. In a study of the host-pathogen relationship it was found that young bean roots, with the radicle just emerging, were highly tolerant to the pathogen, whereas older bean seedlings, with a fully developed root system, were completely susceptible. Investigations by low-temperature scanning electron microscopy demonstrated that significantly fewer spores and hyphae were present on the root surface of young bean seedlings as compared to older ones. A similar pattern of attachment was found when bean roots were inoculated with spores of F. solani f. sp. pisi, a related pathogen causing disease on peas but not on beans. Light microscopic studies showed that F. solani f. sp. pisi did not penetrate the root but rapidly formed thick-walled resting spores on the root surface. F. solani f. sp. phaseoli on the other hand quickly penetrated the root and formed an extensive network of fungal hyphae. These results demonstrate that the ability of fungal propagules to adhere to and to penetrate host tissues are two distinct processes. Furthermore, the data indicate that young bean roots lack a surface component necessary for attachment of fungal spores which may help explain their tolerance to Fusarium root rot.     

Radiometric assessment of tillage and seed treatment effect on soybean root rot caused by Fusarium spp. in central Minnesota

Soybean root rot, caused primarily by Fusarium solani f. sp. phaseoli in a complex with F. oxysporum and Rhizoctonia solani, has become an increasing problem for soybeans, dry beans, and other rotation crops in central Minnesota due to soil conditions associated with reduced tillage. This study was conducted, in two field sites in central Minnesota located near Staples and Verndale, to develop methods for nondestructive assessment of root rot severity using plant radiometric properties. Soybean canopy reflectance was measured with a hand-held multi-spectral radiometer. Prior to the radiometer measurements, attempts were made to create differing root rot situations with moldboard or chisel tillage, and with or without a biological seed treatment. Root rot severity was estimated using a visual disease severity scale. Colony-forming units (CFU) were determined to estimate soil populations of pathogenic F. solani and F. oxysporum. Results from the Verndale site consistently showed significant treatment effects in the measured canopy radiometric parameters, and in the visual disease rating and yield (significant for seed treatment). Values of a simple ratio vegetation index from this site exhibited negative relationships with disease rating and F. oxysporum CFU, and a positive linear relationship with yield. Treatment effects were generally not significant at the Staples site because of low initial F. oxysporum populations. The results indicate that remote sensing is potentially a rapid, nondestructive means for assessment of root rot diseases in soybean.     

Effect of mycorrhiza and biofertilisers on reducing the incidence of Fusarium root and pod rot diseases of peanut

Pathogenicity tests of twenty-six fungal isolates were tested on peanut plants (Giza 5 cv.) and the results revealed that, Fusarium oxysporum isolate (No. I) followed by F. solani (No. II) then F. moniliforme (No III) significantly caused highest incidence of root rot disease. Also, F. moniliforme (No III) followed by F. solani (No II) then F. oxysporum (No I) gave the highest incidence of pod rot disease. The effectiveness of vescular arbuscular-mycorrhiza (VAM) at different application rates on the incidence of root rot, pod rot diseases and plant growth parameters of peanut was studied. All soil treatments with each rate of VAM significantly reduced root and pod rot diseases compared with control (rate 0%). The best reduction in the severity of both diseases with VAM was found at the rate of 3%. Application of rhizobacterin, microbin and cerialin biofertilisers at the different concentrations decreased the severity of both root rot and pod rot severity diseases compared with non-treated seeds. The greatest reduction in both diseases was achieved at a concentration of 8/100?g seeds. The highest number of pods and fresh weight (g) was achieved in seed supplemented with each biofertiliser at concentration of 8/100?g seed.     

Effect of methyl jasmonate (MeJA) on biochemical responses of wheat seedlings infected by Fusarium culmorum

Fusarium culmorum is a ubiquitous soil-borne fungus which is able to cause foot and root rot on different small-grain cereals, in particular wheat and barley. Wheat (Triticum aestivum L.) is among the oldest and most extensively grown of all crops. Systemic acquired resistance (SAR) is a pathogen-induced disease resistance response in plants that is characterized by broad spectrum disease control. SAR is an important component of the disease resistance repertoire of plants. The effect of the resistance inducer, methyl jasmonate (MeJA), was tested by seed-soaking to determine whether this resistance inducer controlled root rot of wheat caused by F. culmorum. MeJA is an inducing disease resistance in a number of dicotyledonous and monocotyledonous plant species. This research has been conducted to determine the effect of MeJA seed treatment on chlorophyll a, chlorophyll b, total protein, peroxidase (POD) enzyme, phenolic compounds and phenylalanine ammonia lyase (PAL) factors. MeJA, which is an important chemical inducer of SAR, can activate resistance to pathogen infection in commercial crops. Seeds treated with MeJA showed an elevation in the total chlorophyll, carotenoid and activity of defence-related enzymes, POD and PAL.     

First report of molecular characterisation of Fusarium proliferatum associated with root rot disease of Indian mulberry (Morinda officinalis How.) in Viet Nam

Root rot is the most serious disease affecting Indian mulberry in Viet Nam. The objective of the present study was to confirm the identities and pathogenicity of species of Fusarium isolated from the roots of Indian mulberry. Based on pathogenicity assays, F. proliferatum was shown to be the pathogenic agent. The identity of F. proliferatum was confirmed by PCR and phylogenetic analyses based on the sequences of the ITS region and the TEF1-α gene. Of four semi-solid media (CA, PDA, CDA and YMA) tested, PDA was the most suitable medium for the growth of F. proliferatum. The optimal temperature range for the growth of F. proliferatum was 20–30?°C with a maximum at growth rate at 25?°C. The optimum pH for growth ranged from pH5.0–6.0 with maximum growth at 5.5. This is the first report of F. proliferatum causing root rot of Indian mulberry in Viet Nam.     

Fusarium Species from the Fusarium fujikuroi Species Complex Involved in Mixed Infections of Maize in Northern Sinaloa,Mexico

Fusarium species belonging to the Fusarium fujikuroi species complex (FFSC) are associated with maize in northern Mexico and cause Fusarium ear and root rot. In order to assess the diversity of FFSC fungal species involved in this destructive disease in Sinaloa, Mexico, a collection of 108 fungal isolates was obtained from maize plants in 2007–2011. DNA sequence analysis of the calmodulin and elongation factor 1α genes identified four species: Fusarium verticillioides, F. nygamai, F. andiyazi and F. thapsinum (comprising 79, 23, 4 and 2 isolates, respectively). Differential distribution of Fusarium species in maize organs was observed, that is F. verticillioides was the most frequently isolated species from maize seeds, while F. nygamai predominated on maize roots. Mixed infections with F. verticillioides/F. thapsinum and F. verticillioides/F. nygamai were detected in maize seeds and roots, respectively. Pathogenicity assay demonstrated the ability of the four species to infect maize seedlings and induce different levels of disease severity, reflecting variation in aggressiveness, plant height and root biomass. Isolates of F. verticillioides and F. nygamai were the most aggressive. These species were able to colonize all root tissues, from the epidermis to the vascular vessels, while infection by F. andiyazi and F. thapsinum was restricted to the epidermis and adjacent cortical cells. This is the first report of F. nygamai, F. andiyazi and F. thapsinum infecting maize in Mexico and co‐infecting with F. verticillioides. Mixed infections should be taken into consideration due to the production and/or accumulation of diverse mycotoxins in maize grain.     

The epidemiology of tomato brown root rot

In the absence of nematodes, three different symptoms of disease, parts of the brown root rot complex (BRR), occurred on tomato roots surviving in soils infested with GSF (= grey sterile fungus) and Colletotrichum atramentarium (Berk. & Br.) Taubenh. In heavily infested soils brown lesions occurred throughout cropping, appearing within a week of planting. Corkiness and black dot, caused by GSF and C. atramentarium respectively, rarely occurred until the third month after planting but towards the end of the season the incidence of black dot sometimes suddenly increased greatly. Observations of crops growing in plots treated with different soil partial sterilants suggested that GSF was more damaging than C. atramentarium. Yield was not related to the incidence of black dot but was inversely proportional to the occurrences of brown lesions and corkiness. The relation with brown lesions was significant within 8 weeks of planting, when most brown lesions gave cultures of GSF, but later more of these lesions gave cultures of C. atramentarium than of GSF. Pathogenicity tests with pure cultures of GSF and C. atramentarium were done on agar media and by artificially infesting partially sterilized soils. Roots of undamaged seedlings on agar media developed 10 mm. brown lesions within 2 weeks of inoculating 10-day-old tomatoes with most GSF cultures isolated from: (1) rotted roots of Lycopersicon esculentum, Solanum capsicastrum, Capsicum annuum var. longum and C. frutescens; (2) browned zones of Lycopersicon hirsutum roots; and (3) apparently healthy roots of Cucumis sativus. After inoculation with C. atramentarium, small (c. 2 mm.) pink lesions developed, whereas none formed using Pyrenochaeta spp. In soil tests the greater root damage done by GSF, including root loss, was reflected in decreased aerial growth and smaller fruit yields; C. atramentarium affected neither. In the second year of soil infestation GSF decreased yields during 6 weeks of picking from 1.96 kg. in the uninoculated controls to 1.02 kg./plant. The pattern of damage done by GSF changed as plants aged. In soil, brown lesions occurred within a few days of planting but corkiness did not appear for 2–3 months, when stem lesions and leaf yellowing often developed simultaneously. A 50% root loss after 21 weeks did not affect fruit yields whereas a 40% loss within 11 weeks of planting was reflected by a 45% yield decrease.     

Bacillus subtilis subsp. spizizenii MB29 controls alfalfa root rot caused by Fusarium semitectum

Medicago sativa L. is the most important forage legume in China. Reducing production losses caused by disease is an essential aspect of maximising alfalfa production. In the current study a Fusarium semitectum isolate collected from alfalfa roots exhibiting symptoms of root rot was proven to infect alfalfa by fulfilling Koch's postulates. A bacterial strain, MB29, also collected from alfalfa roots, was evaluated as a potential biocontrol agent against F. semitectum and a range of other alfalfa pathogens using in vitro tests. It was found that MB29 reduced the mycelia growth of all the pathogens assessed, and in the case of F. semitectum by as much as 84.47%. Furthermore, in vivo test showed that MB29 reduced the severity of rot symptoms in alfalfa seedlings resulting from F. semitectum infection. Strain MB29 was subsequently classified as Bacillus subtilis subsp. spizizenii using the Biolog MicroLog microbial identification system and sequence analysis of its 16S rDNA gene. Taken together these results indicate that B. subtilis subsp. spizizenii MB29 has great potential for the control of root rot diseases in alfalfa.     

Characterisation of husk rot in macadamia

The causal agent of husk rot of macadamia is often attributed to Colletotrichum gloeosporioides sensu lato. However, in recent husk rot outbreaks, the characteristic concentric ring of pycnidia of C. gloeosporioides that is associated with the disease was often absent. Due to its sporadic occurrence, the importance of husk rot is often underrated and attributed to environmental and physiological factors. In order to determine the significance, prevalence and factors that influence husk rot in macadamia, this study examined the aetiology of husk rot in Australia. The relative incidence and severity of husk rot was evaluated in several macadamia orchards over eight consecutive years. Pathogenicity assays were developed to confirm the identity of the causal agent. A range of fungi from several genera including: Diaporthe, Lasiodiplodia, Colletotrichum, Pestalotiopsis, Aspergillus, Alternaria, Nigrospora and Epicoccum were isolated from samples of macadamia pericarps with husk rot symptoms from different orchards. Fungi in the genus Diaporthe were most frequently isolated, often from symptomatic fruit. Results from pathogenicity trials showed the characteristic soft or spongy black lesions characteristic of husk rot symptoms in wounded fruits that were incubated with the diseased fruit or inoculated with a conidial suspension of Diaporthe spp. Our results suggest that injury to the macadamia fruit pericarp not only predisposes the pericarp to pathogen infection but it is a prerequisite for infection. Large variations in husk rot severity were observed over years. Husk rot severity was linked to days after anthesis and was associated with mean weekly relative humidity and minimum temperatures. This study confirmed that Diaporthe species cause husk rot in macadamia, hence, a rationale for adopting Phomopsis husk rot as the name of the disease is discussed.     

Application of Genomic and Quantitative Genetic Tools to Identify Candidate Resistance Genes for Brown Rot Resistance in Peach

The availability of a complete peach genome assembly and three different peach genome sequences created by our group provide new opportunities for application of genomic data and can improve the power of the classical Quantitative Trait Loci (QTL) approaches to identify candidate genes for peach disease resistance. Brown rot caused by Monilinia spp., is the most important fungal disease of stone fruits worldwide. Improved levels of peach fruit rot resistance have been identified in some cultivars and advanced selections developed in the UC Davis and USDA breeding programs. Whole genome sequencing of the Pop-DF parents lead to discovery of high-quality SNP markers for QTL genome scanning in this experimental population. Pop-DF created by crossing a brown rot moderately resistant cultivar ‘Dr. Davis’ and a brown rot resistant introgression line, ‘F8,1–42’, derived from an initial almond × peach interspecific hybrid, was evaluated for brown rot resistance in fruit of harvest maturity over three seasons. Using the SNP linkage map of Pop-DF and phenotypic data collected with inoculated fruit, a genome scan for QTL identified several SNP markers associated with brown rot resistance. Two of these QTLs were placed on linkage group 1, covering a large (physical) region on chromosome 1. The genome scan for QTL and SNP effects predicted several candidate genes associated with disease resistance responses in other host-pathogen systems. Two potential candidate genes, ppa011763m and ppa026453m, may be the genes primarily responsible for M. fructicola recognition in peach, activating both PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI) responses. Our results provide a foundation for further genetic dissection, marker assisted breeding for brown rot resistance, and development of peach cultivars resistant to brown rot.