Alternaria Black Spot of Crucifers: Symptoms, Importance of Disease, and Perspectives of Resistance Breeding

Abstract

Alternaria black spot of cruciferous vegetables, incited by different species of Alternaria, remains an increasing threat to Brassicaceae crops throughout the world, including Poland. Brassica plants are attacked by conidia of A. brassicae (Berk.) Sacc., A. brassicicola (Schw.) Wiltsh., A. raphani Groves & Skolko, and A. alternata (Fr.) Kreissler. The pathogens have a wide spectrum of hosts, such as head cabbage, Chinese cabbage, cauliflower, broccoli, and other crucifers including cultivated and wild grown plants.Alternaria pathogens usually cause damping-off of seedlings, spotting of leaves of cabbages, blackleg of heads of cabbages, and spotting of cauliflower curds and broccoli florets. In oilseed rape, A. brassicae is the dominant invasive species, while in the cruciferous vegetables, both species, A. brassicae, and A. brassicicola are encountered. Infected seeds with spores on the seed coat or mycelium under the seed coat are the main means of distribution for these pathogens. The fungus can overwinter on susceptible weeds or crop debris and on seed plants, as well as on stecklings.Methods for disease prevention and control are based on combining agricultural management practices with chemical control. Using disease-free seeds or seeds treated with fungicides can greatly reduce disease incidence. After appearance of the first symptoms of disease, stringent fungicide spray program is an effective way to reduce losses. Many authors seem to agree, that the most economically feasible method of disease control is the development of resistant Brassicaceae crops varieties, as transgenic approach proved unsuccessful. Due to our increasing understanding of pathogen-host plant interactions, identification of resistance sources, and assessment of the resistance trait inheritance mode, breeding programs of Brassica crops for Alternaria resistance can be enhanced. This is of particular importance since recent years experience dynamic development of ecological and integrated plant production with an emphasis on plant biotic stress resistance. Highly resistant genetic resources have not been reported in Brassica cultivated species, although some varieties differ in their resistance/susceptibility level. 6 VEGETABLE CROPS RESEARCH BULLETIN 76 _____________________________________________________________________________________________________ Strong cross-incompatibility, polygenic background of the resistance (additive and dominant gene interactions), as well as the differences in ploidy between the Brassica species of interest, render the transfer of Alternaria resistance from the wild species into the cultivated forms difficult. Additionally, it is often connected with employment of in vitro hybridization techniques, including somatic hybridization, embryo and ovary rescue, or protoplast fusion.

Arabidopsis ABCG34 contributes to defense against necrotrophic pathogens by mediating the secretion of camalexin

“…Our data revealed that AtABCG34 is an important factor required for defense against the necrotrophic fungal pathogens A. brassicicola and B. cinerea and that AtABCG34 functions by secreting camalexin to the surface. A. brassicicola infection results in dark leaf spots on most Brassica species, including economically important oilseed crops (50). Infection by A. brassicicola considerably reduces the quality and quantity of harvested Brassica crops (51), resulting in annual yield losses of 15-70% (51).…”

Biocontrol Potential of Streptomyces hydrogenans Strain DH16 toward Alternaria brassicicola to Control Damping Off and Black Leaf Spot of Raphanus sativus

“…Typical disease signs consist of black lesions on seedlings, leaves, stems, and siliquae resulting in accelerated senescence, premature pod shatter, and shrunken seeds (Mac Kinon et al, 1999; Iacomi-Vasilescu et al, 2004). Seeds infected with the pathogen result in reduced seed germination, photosynthetic potential, seedling vigor and pre- and post-emergence damping-off of seedlings (Nowicki et al, 2012), causing significant reduction in yield quantity and quality.…”

Quantification of Alternaria brassicicola infection in the Arabidopsis thaliana and Brassica rapa subsp. pekinensis

“…Alternaria brassicicola is a necrotrophic fungal pathogen that causes black spot disease in many cruciferous vegetables, such as broccoli, cabbage, cauliflower, radish and turnip (Nowicki et al, 2012;Otani et al, 1995). A recent survey reported that vegetable crop losses caused by this fungus might be 20-80 % worldwide (Nowicki et al, 2012).…”

“…A recent survey reported that vegetable crop losses caused by this fungus might be 20-80 % worldwide (Nowicki et al, 2012). In addition to its economic importance, the interaction between this pathogen and several ecotypes or mutants of Arabidopsis thaliana has been used as a model system to investigate functions of fungal virulence factors and plant genes and signals modulating disease progression.…”