Int.J.Curr.Microbiol.App.Sci (2014) 3(4): 113-124 ISSN: 2319-7706 Volume 3 Number 4 (2014) pp. 113-124 http://www.ijcmas.com Review Article Citrus Melanose (Diaporthe citri Wolf): A Review K.Gopal*, L. Mukunda Lakshmi, G. Sarada, T. Nagalakshmi, T. Gouri Sankar, V. Gopi and K.T.V. Ramana Dr. Y.S.R. Horticultural University, Citrus Research Station, Tirupati-517502, Andhra Pradesh, India *Corresponding author A B S T R A C T K e y w o r d s Citrus Melanose disease caused by Diaporthe citri Wolf is a fungus that causes two distinct diseases on Citrus species viz, the perfect stage of the fungus causes Citrus melanose, disease characterized by lesions on fruit and foliage and in the imperfect Melanose; stage; it causes Phomopsis stem-end rot, a post-harvest disease. It is one of the Diaporthe most commonly observed diseases of citrus worldwide. As the disease is occurring citri; in larger proportions and reducing marketable fruit yield hence, updated post-harvest information on its history of occurrence, disease distribution and its impact, disease pathogen and its morphology, disease symptoms, epidemiology and management are briefly reviewed in this paper. Introduction Citrus Melanose occurs in many citrus fungus does not normally affect the pulp. growing regions of the world and infects On leaves, the small, black, raised lesions many citrus species. It affects young are often surrounded by yellow halos and leaves and fruits of certain citrus species can cause leaf distortion. On the fruit, the or varieties when the tissues grow and disease produces a superficial blemish expand during extended periods of rainy which is unlikely to affect the overall yield or humid weather conditions. The of processing fruit, but causes external symptoms of this widely distributed fungal blemishes which reduce the value of fruit disease vary from small spots or scab-like intended for the fresh market. This disease lesions to patterns of damage referred to as is generally of minor economic importance tear-drop, mudcake, and star melanose. on foliage. All commercial citrus varieties This is one of the most commonly grown in Florida are susceptible to observed diseases of citrus fruits melanose. Pustules are larger on worldwide. Citrus melanose is caused by grapefruit, so blemishes tend to be more the plant-pathogenic fungus Diaporthe serious on this species. The disease citri (anamorph = Phomopsis citri). It can typically attacks sweet orange (Citrus create severe fruit rind blemishes, but the sinensis), grapefruit (C. paradisi) and 113 Int.J.Curr.Microbiol.App.Sci (2014) 3(4): 113-124 pummelo (C. grandis). The disease inoculum, and from pure cultures of P. reduces the aesthetic quality of fresh fruits citri both melanose and stem-end rot could for the market, although it does not affect be reproduced on citrus plants. Fawett edibility. (1932) compared isolates of P. citri and D. citri from across the globe as well as P. History, Taxonomy and Phylogeny californica and found the teleomorphs indistinguishable. Eight years later Ruehle Diaporthe citri Wolf and Kuntz (1940) showed that the spores (anamorph: Phomopsis citri Fawc.) is a of both P. citri and D. citri caused fungus that causes two distinct diseases melanose on citrus leaves. on Citrus species. In the perfect stage, this fungus causes melanose, disease Because the name Diaporthe citri has been characterized by superficial fruit and foliar applied to melanose and stem rot disease lesions, and in the imperfect stage, it of Citrus for decades and Fawcett (l.c.) causes Phomopsis stem-end rot, a post- explicitly stated that he was unaware of harvest disease (Whiteside, 1988). While any previous Diaporthe or Phomopsis on melanose was first found and described by Citrus, it is proposed that Phomopsis citri Swingle and Webber in 1892 near Citra, H.S. Fawc. be conserved against its earlier Florida (Wolf, 1926), it wasn t until 1928 homonym P. citri (Sacc.) Traverso & that Koch s postulates were completed Spessa.This will make the former name and Diaporthe citri was confirmed as the available as a basionym for Diaporthe citri causal agent of melanose on citrus (Bach (H.S. Fawc.) F.A. Wolf, giving this name and Wolf, 1928). In 1912, Fawcett priority over what would otherwise be the proposed the causal agent of stem-end rot earlier taxonomic synonyms D. citrincola as P. citri. Descriptions of two pathogens and Phomopsis caribaea, both of which belonging to the genus Phomopsis that predate the currently first legitimate caused stem-end rot on citrus were publication as Diaporthe citri F.A. Wolf. published in 1922, and they were given As no type material of P. citri was found different species names because of at either BPI or FLAS, leaving only an differences in growth characteristics in illustration (Fawcett, l.c.) as a potential, vitro and pathogenicity in planta. The first but unsatisfactory, iconotype, a recent was discovered in the Isle of Pines, West specimen from diseased Citrus sp. Hence, Indies, in 1917, on grape fruit, and the it is proposed as a conserved type for name P. caribaea was proposed by the Phomopsis citri (Amy Rossman et al author (Horne, 1922). The second was 2013). found in 1919 in California on lemons. The fungus was tentatively named P. Another synonymous species of D. californica (Fawcett, 1922).The first citri is D. medusaea Nitschke, and because evidence that these two diseases melanose the latter species was described first, and stem-end rot - were caused by the Fisher proposed in 1972 that the name D. same fungus was published by Floyd and medusaea should take precedence over D. Stevens in 1912. The authors were unable citri. In the same article, Fisher proposed to isolate any fungus from melanose that because P. cytosporella was described infected leaves, but could reproduce prior to P. citri, the former name should be classic symptoms of melanose by using used. This nomenclature was never washings of stem-end rot affected twigs as adopted. The genus Diaporthe/ Phomopsis 114 Int.J.Curr.Microbiol.App.Sci (2014) 3(4): 113-124 belongs to the phylum Ascomycota, tef1- , tubulin and calmodulin grouped class Sordariomycetes, order Diaporthales, eight most discrepant strains into three and family Diaporthaceae (James et al. distinctive clusters, cluster 1 (Rc001, 2006; Rossman et al. 2007). Combining Eu004 and Eu009), cluster 2 (ZJWCF252, morphological, cultural and molecular Sjm001 and Ac001) and cluster 3 (Pcs013 data, four species were distinguished from and Sfp005) respectively with high F. vulgare. Diaporthe angelicae is shown support values. This cluster above to be the most common pathogen of this represent three potentially novel species host in Portugal. Diaporthe lusitanicae is provides strong evidence of high newly described, whereas the teleomorph biodiversity and novelty of Phomopsis theicola was revealed to be of Diaporthe endophytes from southeast distinct from Diaporthe theicola, and is China (Jiaying Wang et al 2014). Six new described as Diaporthe neotheicola species of Diaporthe, D. beilharziae (Santos and Phillips, 2009). To date, on Indigofera australis, D. fraxini- several molecular phylogenetic studies on angustifoliae on Fraxinus angustifolia genera within the Diaporthales have been subsp. oxycarpa, D. litchicola on Litchi published (Zhang and Blackwell, 2001; chinensis, D. nothofagi on Nothofagus Castlebury et al. 2002; Udayanga et al. cunninghamii, D. pascoei on Persea 2011; Udayanga et al. 2012) but none americana and D. salicicola on Salix have included D. citri/P. citri. Among the purpurea from Australia are described and eight described families within illustrated based on morphological the Diaporthales, the family most related characteristics and molecular analyses to Diaporthaceae is likely Valsaceae (Tan et al; 2013). (Castlebury et al. 2002). Although species of Diaporthe have in the past chiefly been Symptoms distinguished based on host association, Gomes et al (2013) studies confirm Melanose on Leaves: Symptoms on several taxa to have wide host ranges, foliage begin as tiny water-soaked specks suggesting that they move freely among that become depressed in the center and hosts, frequently co-colonising diseased or surrounded by a translucent yellow area dead tissue. In contrast, some plant which is not depressed. Later, the leaf pathogenic and endophytic taxa appear to cuticle ruptures and a gummy substance is be strictly host specific. Given this diverse exuded which turns brown and hardens. ecological behaviour among members of The yellowish margin disappears and the Diaporthe, future species descriptions hardened gummed areas will have a lacking molecular data should be strongly sandpaper-like texture. Infected areas on discouraged (Gomes et al. 2013). Multi- the leaf may be scattered, aggregated, or in locus phylogeny based on combined streaks, depending on where water sequences of rDNA ITS, and partial transported the inoculums prior to sequences from the translation elongation infection. Severely infected leaves become factor 1- , tubulin and calmodulin pale green to yellow, can be distorted and genes, reveal three new species, Diaporthe fall from the tree. Melanose is seldom siamensis, D. thunbergii and D. severe on the spring growth flush. When it pterocarpicola from Thailand (Dhanushka does occur on this flush, the pustules are Udayanga et al; 2012). Multi-gene usually few and little or no leaf drop phylogenetic analysis based on ITS rDNA, occurs (Fig. 1). On the summer growth 115 Int.J.Curr.Microbiol.App.Sci (2014) 3(4): 113-124 flushes, melanose can be severe enough to about 80 countries. Further, seven of the cause defoliation, particularly in years ten highest citrus producing countries are following freeze-induced twig die-back. reported to have D. citri (FAOSTAT, On fruit there is a tendency for the 2010). Fruit severely affected by melanose diseased areas to form tear-streak and is not marketable as fresh fruit and water droplet patterns.