Diagnosis of pine wilt disease using remote wireless sensing

Pine wilt disease caused by Bursaphelenchus xylophilus is a major tree disease that threatens pine forests worldwide. To diagnose this disease, we developed battery-powered remote sensing devices capable of long-range (LoRa) communication and installed them in pine trees (Pinus densiflora) in Gyeongju and Ulsan, South Korea. Upon analyzing the collected tree sensing signals, which represented stem resistance, we found that the mean absolute deviation (MAD) of the sensing signals was useful for distinguishing between uninfected and infected trees. The MAD of infected trees was greater than that of uninfected trees from August of the year, and in the two-dimensional plane, consisting of the MAD value in July and that in October, the infected and uninfected trees were separated by the first-order boundary line generated using linear discriminant analysis. It was also observed that wood moisture content and precipitation affected MAD. This is the first study to diagnose pine wilt disease using remote sensors attached to trees.

CmPMRl and CmPMrs Were Responsible for Resistance to Powdery Mildew Caused by Podosphaera Xanthii Race 1 in Melon

Cucumis melo L. is an economically important crop, the production of which is threatened by the prevalence of melon powdery mildew (PM) infections. We herein utilized the MR-1 (P1; resistant to PM) and M4-7 (P2; susceptible to PM) accessions to assess the heritability of PM (race 1) resistance in these melon plants. PM resistance in MR-1 leaves was linked to a dominant gene (CmPMRl), whereas stem resistance was under the control of a recessive gene (CmPMrs), with the dominant gene having an epistatic effect on the recessive gene. The CmPMRl gene was mapped to a 50 Kb interval on chromosome 12, while CmPMrs was mapped to an 89 Kb interval on chromosome 10. The CmPMRl candidate gene MELO3C002441 and the CmPMrs candidate gene MELO3C012438 were identified through sequence alignment, functional annotation, and expression pattern analyses of all genes within these respective intervals. MELO3C002441 and MELO3C012438 were both localized to the cellular membrane and were contained conserved NPR gene-like and MLO domains, respectively, which were linked to PM resistance. In summary, we identified patterns of PM resistance in the disease-resistant MR-1 melon cultivar, and conducted finally-mapping to identify two putative genes linked to resistance. Our results offer new genetic resources and markers guide the future molecular marker-assisted breeding of PM-resistant melon.

Quantitative Inheritance of Sclerotinia Stem Rot Resistance in Brassica napus and Relationship to Cotyledon and Leaf Resistances

Sclerotinia sclerotiorum is a necrotrophic fungus causing devastating stem rot and associated yield losses of canola/rapeseed (Brassica napus) worldwide, including in Australia. Developing host resistance against Sclerotinia stem rot is critical if this disease in canola/rapeseed is to be successfully managed, as cultural or chemical control options provide only partial or sporadic control. Three B. napus breeding populations, C2, C5 and C6, including the parents, F1, F2, BC1P1 and BC2P2, were utilised in a field study with an objective of exploring the inheritance pattern of disease resistance (based on stem lesion length, SLL), the genetic relationships of disease with stem diameter (SD) or days to flowering (DTF), and to compare these new adult plant stem resistances against S. sclerotiorum with those of seedling (cotyledon and leaf) resistances in earlier studies. Heritability (broad-sense) of SLL, was 0.57 and 0.73 for populations C2 at 3 and 5 weeks post-inoculation, and was 0.21 for C5 at 5 weeks post-inoculation. Additive genetic variance was evident within all three populations for DTF but not for SD. Narrow sense heritability for DTF was 0.48 (C2), 0.42 (C5) and 0.32 (C6). SD, DTF and SLL were all inherited independently with no significant genetic covariance between traits in bivariate analysis. Genetic variance for SLL in populations C2 and C5 was entirely non-additive, and there was significant non-additive genetic covariance of SLL at 3 and 5 weeks post-inoculation. Generation means analysis in population C2 supported the conclusion that complex epistatic interactions controlled SLL. Several C2 and C5 progeny showed high adult plant stem resistance which may be critical in developing enhanced stem resistance in canola/rapeseed. While population C6 showed no genetic variation for SLL resistance in this study, it showed significant non-additive genetic variance at the cotyledon and leaf stages in earlier studies. We conclude that host resistance varies across different plant growth stages and breeding must be targeted for resistance at each growth stage. In populations C2, C5 and C6, resistance to S. sclerotiorum in stem, leaf and cotyledon is always controlled by non-additive effects such as complex epistasis or dominance. Overall, our findings in relation to the quantitative inheritance of Sclerotinia stem rot resistance, together with the new, high-level resistances identified, will enable breeders to select/develop genotypes with enhanced resistances to S. sclerotiorum.

Identification of sources of Sclerotinia sclerotiorum resistance in a collection of wild Cicer germplasm

Sclerotinia sclerotiorum is an important fungal pathogen of chickpea (Cicer arietinum L.) and it can cause yield losses up to 100%. The wild progenitors are much more diverse than domesticated chickpea and this study describes how this relates to S. sclerotiorum resistance. Initially, the pathogenicity of nine Australian S. sclerotiorum isolates was examined on three Cicer lines to develop a robust phenotyping assay and significant differences in isolate aggressiveness were identified with 6 isolates being classed as highly aggressive and 3 as moderately aggressive. We identified two S. sclerotiorum isolates, CU8.20 and CU10.12, to be highly aggressive and moderately aggressive, respectively. A subsequent phenotyping assay was conducted using the two isolates to evaluate 86 wild Cicer accessions (Cicer reticulatum and Cicer echinospermum) and two C. arietinum varieties for resistance to S. sclerotiorum. A subset of 12 genotypes was further evaluated, and subsequently, two wild Cicer accessions with consistently high levels of resistance to S. sclerotiorum were examined using the initially characterised nine isolates. Wild Cicer accessions Karab_084 and Deste_063 demonstrated consistent partial resistance to S. sclerotiorum. There were significant differences in responses to S. sclerotiorum across wild Cicer collection sites. The Cermik, Karabahce and Destek sites’ responses to the aggressive isolate CU8.20 ranged from resistant to susceptible, highlighting an interaction between isolate genotype and chickpea collection site for sclerotinia stem rot resistance. This is the first evidence of partial stem resistance identified in wild Cicer germplasm, which can be adopted in chickpea breeding programs to enhance S. sclerotiorum resistance in future chickpea varieties.

Xylem network connectivity and embolism spread in grapevine(Vitis vinifera L.)

Xylem networks are vulnerable to the formation and spread of gas embolisms that reduce water transport. Embolisms spread through interconduit pits, but the three-dimensional (3D) complexity and scale of xylem networks means that the functional implications of intervessel connections are not well understood. Here, xylem networks of grapevine (Vitis vinifera L.) were reconstructed from 3D high-resolution X-ray micro-computed tomography (microCT) images. Xylem network performance was then modeled to simulate loss of hydraulic conductivity under increasingly negative xylem sap pressure simulating drought stress conditions. We also considered the sensitivity of xylem network performance to changes in key network parameters. We found that the mean pit area per intervessel connection was constant across 10 networks from three, 1.5-m stem segments, but short (0.5 cm) segments fail to capture complete network connectivity. Simulations showed that network organization imparted additional resistance to embolism spread beyond the air-seeding threshold of pit membranes. Xylem network vulnerability to embolism spread was most sensitive to variation in the number and location of vessels that were initially embolized and pit membrane vulnerability. Our results show that xylem network organization can increase stem resistance to embolism spread by 40% (0.66 MPa) and challenge the notion that a single embolism can spread rapidly throughout an entire xylem network.

Elastic Modulus Is an Ideal Indicator to Evaluate Maize Stem Strength

Background: Stem lodging seriously restricts the development of mechanized maize harvesting. However, currently there is no comprehensive stem strength evaluation standard for cultivating new maize varieties with excellent stem performance that are suitable for mechanical harvesting. In this study, we constructed a panel of maize germplasm accessions with various stem strengths by setting up different levels of stalk-rot resistance. We investigated the factors influencing maize stem strength, as well as the relationships among them to clarify the key indices for evaluating stem strength. Results: Our results indicated that the stem density, moisture content, bending strength and rind puncture strength were responsive to stalk-rot resistance. However, these indices were in agreement with stem resistance only after the physiological maturity of maize. In particular, the stem rind puncture strength exhibited a closer correlation with the stem resistance in the late stage of physiological maturity. It was also demonstrated that stem density directly affected bending strength and rind puncture strength, whereas indirectly affected the elastic modulus. The elastic modulus includes both load and displacement; therefore, it can prompt the reliability of stem strength evaluation, and is the best description of stalk toughness. The attenuation amplitude of the elastic modulus is always the largest whether it is caused by the aggravation of the disease, the growth stage delay, or the internode position rise, which significantly improves the sensitivity of stalk strength evaluation. Our results showed that the elastic modulus was correspondent with stem resistance from the silking stage of maize, which not only effectively improved the accuracy of the stalk strength evaluation, but also was extremely beneficial to improve the efficiency of maize variety selection. Conclusions: The elastic modulus can be used to evaluate the maize stem strength truly and accurately, and especially in the high stalk rot incidence region, it is very beneficial to improve the breeding efficiency of the maize varieties suitable for mechanical harvesting.

Resistance of New Zealand Provenance Leptospermum scoparium, Kunzea robusta, Kunzea linearis, and Metrosideros excelsa to Austropuccinia psidii

Resistance to the pandemic strain of Austropuccinia psidii was identified in New Zealand provenance Leptospermum scoparium, Kunzea robusta, and K. linearis plants. Only 1 Metrosideros excelsa-resistant plant was found (of the 570 tested) and no resistant plants of either Lophomyrtus bullata or L. obcordata were found. Three types of resistance were identified in Leptospermum scoparium. The first two, a putative immune response and a hypersensitive response, are leaf resistance mechanisms found in other myrtaceous species while on the lateral and main stems a putative immune stem resistance was also observed. Both leaf and stem infection were found on K. robusta and K. linearis plants as well as branch tip dieback that developed on almost 50% of the plants. L. scoparium, K. robusta, and K. linearis are the first myrtaceous species where consistent infection of stems has been observed in artificial inoculation trials. This new finding and the first observation of significant branch tip dieback of plants of the two Kunzea spp. resulted in the development of two new myrtle rust disease severity assessment scales. Significant seed family and provenance effects were found in L. scoparium, K. robusta, and K. linearis: some families produced significantly more plants with leaf, stem, and (in Kunzea spp.) branch tip dieback resistance, and provenances provided different percentages of resistant families and plants. The distribution of the disease symptoms on plants from the same seed family, and between plants from different seed families, suggested that the leaf, stem, and branch tip dieback resistances were the result of independent disease resistance mechanisms.

Comparative Reaction of Camelina sativa to Sclerotinia sclerotiorum and Leptosphaeria maculans

Sclerotinia sclerotiorum and Leptosphaeria maculans are two of the most important pathogens of many cruciferous crops. The reaction of 30 genotypes of Camelina sativa (false flax) was determined against both pathogens. C. sativa genotypes were inoculated at seedling and adult stages with two pathotypes of S. sclerotiorum, highly virulent MBRS-1 and less virulent WW-1. There were significant differences (P < 0.001) among genotypes, between pathotypes, and a significant interaction between genotypes and pathotypes in relation to percent cotyledon disease index (% CDI) and stem lesion length. Genotypes 370 (% CDI 20.5, stem lesion length 1.8 cm) and 253 (% CDI 24.8, stem lesion length 1.4 cm) not only consistently exhibited cotyledon and stem resistance, in contrast to susceptible genotype 2305 (% CDI 37.7, stem lesion length 7.2 cm), but their resistance was independent to S. sclerotiorum pathotype. A F5-recombinant inbred line population was developed from genotypes 370 × 2305 and responses characterized. Low broad-sense heritability indicated a complex pattern of inheritance of resistance to S. sclerotiorum. Six isolates of L. maculans, covering combinations of five different avirulent loci (i.e., five different races), were tested on C. sativa cotyledons across two experiments. There was a high level of resistance, with % CDI < 17, and including development of a hypersensitive reaction. This is the first report of variable reaction of C. sativa to different races of L. maculans and the first demonstrating comparative reactions of C. sativa to S. sclerotiorum and L. maculans. This study not only provides new understanding of these comparative resistances in C. sativa, but highlights their potential as new sources of resistance, both for crucifer disease-resistance breeding in general and to enable broader adoption of C. sativa as a more sustainable oilseed crop in its own right.

Development of F1 hybrids of cabbage with complex resistance in the south of Russia

Relevance Breeding for resistance is one of the priorities when working with late-ripening cabbage.The most significant damage to this crop in the south of Russia is caused by diseases such as fusarium, black rot, and from pests – tobacco trips. Methods The purpose of the research is development of heat-resistant hybrids of medium-late and late maturity of various areas of use with complex resistance. For 2 decades much attention was paid to breeding and immunological work on development of inbred lines with group resistance: to fusarium and polygenic resistance to black rot. The study of race-specific resistance for better protection against black rot began in 2013. At that, the progeny of the lines were eveluated, which were selected by hydathogenic polygenic resistance on the infectious background of cabbage during inoculation of plants with the Krasnodar population of the pathogen.Since specific resistance to a particular race inherited in white cabbage is recessive and it is very difficult to develop lines and hybrids resistant to several races, a strategy was chosen to increase resistance to this dangerous disease based on a combination of field resistance, stem resistance to the main race 1 and leaf resistance to one or two races. Results As a result of the work carried out in 2018, 44 lines of medium-late maturity with stem resistance to race 1 were selected, of which a significant part of the lines had leaf resistance to a particular race, including 4 lines resistant to races 1 and 4, 1 line – to races 0, 1,4, and 1 line – to races 0, 3, 4. The heat-resistant hybrid for processing Sudarynya was passed to State Variety Testing, it has one parent with stem resistance to race 1, leaf resistance to races 0, 1.4 and hydatode resistance, and the second parent has stem resistance to race 1 and hydatode resistance. Every year, hybrids are evaluated for thrips damage. According to the results of the evaluation of hybrids, lines with a high tolerance to tobacco thrips were identified. In 2017-2018 9 lines with complex resistance to fusarium, black rot and thrips (Ten211, Yas111, Eubi122, Hn861, Hn270-21, Hn270-24, Br272-22, Hn270-14p-1, 272-510) were selected, on the basis of which promising combinations of economically valuable traits were obtained.