A co-inoculation technique to rapidly screen citrus hybrids for resistance to both Alternaria Brown Spot caused by Alternaria alternata and Citrus Scab caused by Elsinoë fawcettii

Smith, Malcolm W.; Gultzow, Debra Lorraine; Newman, Toni K.; Parfitt, S. Carola; Miles, A. K.

doi:10.4322/crt.icc043

Cited by 3 publications

(1 citation statement)

References 2 publications

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“…Keissl. (Pegg, 1966), and citrus scab incited by Elsino€ e fawcettii Bitancourt and Jenkins (Timmer et al, 1996), which has been possible because of the large-scale screening of young seedlings based on the rapid expression of disease symptoms on leaves instead of fruit (Miles et al, 2015;Smith et al, 2016). Consequently, the next major step forward in breeding for CBS resistance will most likely come from the development of a leaf-based screening approach to identify immune or resistant individuals.…”

Section: Discussionmentioning

confidence: 99%

Identification of Resistance to Citrus Black Spot Using a Novel In-field Inoculation Assay

Miles¹,

Smith²,

Tran³

et al. 2019

horts

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Citrus black spot is an important fungal disease of citrus resulting in fruit drop and rind blemish in tropical and subtropical production areas. The disease is incited by the fungus Phyllosticta citricarpa (McAlpine) van der Aa (synonym: Guignardia citricarpa Kiely), with control currently relying on the application of fungicides. Because the presence and expression of resistance is poorly understood, we sought to develop a method for inoculating fruit in the field that gives reproducible symptoms of citrus black spot consistent with natural field infection. We subsequently validated this method by screening 49 citrus accessions and characterized their qualitative expression of citrus black spot symptoms. Challenge inoculations were undertaken with a known isolate of P. citricarpa, and control fruit were inoculated with water or the endophyte P. paracapitalensis Guarnaccia & Crous. Our results showed that all mandarin, sweet orange, lemon and papeda types were susceptible; pummelo, lime, and sour orange types expressed immunity; while various hybrids were susceptible, resistant and immune. Hybrid progeny from crosses using pummelo [Citrus maxima (Burm.) Merr.] as a parent showed preliminary evidence of segregation for citrus black spot immunity. The implications of these results to achieve genetic improvement for citrus black spot resistance in citrus breeding programs are discussed.

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Section: Discussionmentioning

confidence: 99%

Identification of Resistance to Citrus Black Spot Using a Novel In-field Inoculation Assay

Miles¹,

Smith²,

Tran³

et al. 2019

horts

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Pathogenicity ofPhyllosticta citricarpaAscospores onCitrusspp.

Tran

Miles

Smith³

et al. 2018

Plant Disease

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Citrus black spot, caused by Phyllosticta citricarpa, is one of the most important fungal diseases in many citrus-growing regions with hot and humid summers. Ascospores and conidia are known to contribute to epidemic development of the disease. However, pathogenicity testing has never been done for pure ascospores produced from fully characterized P. citricarpa isolates, due to the inability to induce the sexual state in vitro. Recently, an in vitro mating technique was developed to readily produce pure P. citricarpa ascospores for use in host inoculation studies. To test the pathogenicity of P. citricarpa ascospores, we inoculated Troyer citrange leaves and Murcott tangor fruit with ascospores produced in vitro from characterized P. citricarpa isolates. Typical symptoms of citrus black spot occurred. Recovery of P. citricarpa isolates from symptomatic lesions and their characterization using genetic markers enabled us to identify recombinant genotypes among the isolates recovered from ascospore inoculations and, as such, fulfill Koch’s postulates for ascospores. We have also identified Troyer citrange seedlings as a potential model system for citrus black spot inoculation studies, because it allows typical symptoms of citrus black spot to be expressed with a much shorter latent period than on fruit. This will facilitate future studies of epidemiological aspects of P. citricarpa ascospores relative to conidia and improve our understanding of the citrus black spot pathosystem. The susceptibility of Troyer citrange seedlings will also facilitate experimenting with disease management methods, aimed at reducing the impact of citrus black spot.

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Inoculum sources and management of bean scab caused by Elsinoë phaseoli

Masheti,

Muthomi,

Muiru

et al. 2024

Journal of Phytopathology

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Bean scab caused by Elsinoë phaseoli is a major challenge to common bean cultivation in Kenya. However, knowledge about its epidemiology and management is limited. This study conducted three experiments in Kakamega, Kenya, evaluating scab inoculum sources and control options. The first experiment evaluated three different inoculum sources over two seasons; bean crop residue caused the highest scab incidence in both the 2021 (62.1%) and 2022 (81.1%) seasons. The second experiment assessed the effect of rotation history on scab over three seasons. Scab incidence consistently surpassed 90% within the first 30 days after planting in half‐yearly rotated fields across all seasons, while the disease was absent after planting in fields with no recent history of legumes. Fields rotated out of legumes consistently had the highest grain yield, averaging 1.5 t ha−1 over the seasons. Additionally, the rotation land treatment displayed significantly more pods per plant during the 2021 (9.7), 2022a (9.8), and 2022b (12.5) seasons. In the third experiment, the impact of five fungicides and four cropping systems on bean scab was investigated over two seasons. Neither fungicide treatments nor cropping systems had an effect on bean scab incidence even when only severe symptoms were considered. Carbendazim had the highest yield (1.9 t ha−1) outperforming the unsprayed control only in the 2022 season while none of the other fungicides outperformed the control treatment in yield parameters in either season. This study emphasizes the challenge of managing bean scab without proper crop rotation and underscores the role of crop residue as a critical inoculum source.

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A co-inoculation technique to rapidly screen citrus hybrids for resistance to both Alternaria Brown Spot caused by Alternaria alternata and Citrus Scab caused by Elsinoë fawcettii

Cited by 3 publications

References 2 publications

Identification of Resistance to Citrus Black Spot Using a Novel In-field Inoculation Assay

Identification of Resistance to Citrus Black Spot Using a Novel In-field Inoculation Assay

Pathogenicity ofPhyllosticta citricarpaAscospores onCitrusspp.

Inoculum sources and management of bean scab caused by Elsinoë phaseoli

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