BLACK SPOT SYMPTOMS IN BRAZIL

Cracked spot Early virulent spot symptoms

Mixture of hard spot lesions with the black borders and gray centers, and virulent spot symptoms – the reddish spreading Hard spot lesions symptoms

Citrus black spot and sweet scab

By L. W. Timmer, N.A. Peres New approaches spread by rain splash. The disease and J.W. Hyun not only results in unsightly blem - for dealing with ishes on the fruit, but fruit can fall he Florida citrus industry is prematurely, reducing yields. The currently struggling with disease is widespread in Asia and canker and greening. But there two more Australia and has become common in are other diseases around the world Brazil and Argentina since its discov - Tthat may cause further concern. With exotic diseases ery many years ago. Hopefully the all the traffic and movement of peo - disease won’t follow canker and ple worldwide to Florida, the risk of greening and become a problem in introducing more diseases and pests lar to that of greasy spot in that it Florida as well. is high. To avoid further problems, produces airborne spores in the Another potentially problematic we need to protect the industry by litter beneath the tree canopy. The fungal disease is sweet orange scab, developing methods and approaches asexual spores are produced on hard caused by Elsinoe australis . Sweet to prevent introduction and for the spot lesions on fruit and those are orange scab produces symptoms simi - early detection of these lar to citrus scab, but af - diseases if introduced. fects only the fruit of One potential problem sweet oranges and some is citrus black spot, . The scab re - caused by the , duces the external qual - citricarpa . ity of these varieties, but Black spot produces sev - does not affect yield. eral types of symptoms on Sweet orange scab, fruit, such as hard spot, which occurs only in virulent spot, cracked southern South America, spot and false melanose. is controlled by fungi - can be affected as cidal sprays used for well, but only occasional common citrus scab on spots are produced. Sweet orange scab and tanger - The life cycle is simi - on a Valencia in Brazil ines. However, we CITRUS INDUSTRY • February 2007 would prefer not to deal with scab on type of the common citrus scab ing the two species causing scab. The more citrus types than we do currently. pathogen, E. fawcettii , known as the PCR method we developed is able to IDENTIFICATION Florida Broad Host Range pathotype. identify not only the two widespread Because this pathotype can occasion - species causing scab on citrus, but There are complications in identi - ally affect sweet orange fruit, it is also a pathotype of E. australis that fying either of these diseases. Black necessary to isolate this very slow- affects natsudaidai in Korea (J.W. spot is readily identified if typical growing fungus and conduct inocula - Hyun, et al. Plant Disease, accepted). hard spot lesions are present on fruit tion or molecular studies to identify The procedure is effective not only and the fungus is sporulating in those the pathogen. using mycelium of the fungus from spots. However, black spot has many Rapid techniques are needed by culture, but also using lesions directly symptoms such as false melanose and the regulatory agencies to identify from fruit. Thus, we can now identify cracked spot that can be confused these pathogens. Without such meth - the pathogen on affected fruit in one with other problems. In addition, the ods, introductions of dangerous dis - day using plant material directly. fungus is not easily isolated and eases can occur or costly delays and Most of the work was conducted in grows rather slowly. To further com - misidentification of symptoms on Korea by the group of J.W. Hyun, plicate matters, any injuries or scars fruit can occur in ports of entry or in who has a worldwide collection of on fruit unrelated to diseases can be the field. isolates of Elsinoe from citrus. This colonized by the saprophytic species, For the last several years, we have work was funded by the Korea Rural G. mangiferae , which is cosmopolitan been conducting research to improve Development Administration. on many plants including citrus. That detection techniques for these These procedures will be useful to species is found commonly in Florida pathogens. Some molecular tech - regulatory agencies for diagnosis of citrus groves. niques were available for detection diseases encountered on fruit in ports In fact, a few years ago, a load of and differentiation of G. mangiferae as well as for identification of sus - fruit from Florida was rejected at the and G. citricarpa , but those required pect symptoms found in the field. In port in the Netherlands because it pre - large amounts of tissue or lengthy addition, they will be valuable to in - sumably had black spot. Eventually, it extraction procedures. A polymerase vestigators for determining which was demonstrated that the fungus that chain reaction (PCR) procedure we pathogens are responsible for specific had been isolated was G. mangiferae , have developed can be done using a symptoms found on different plant which posed no threat, but it required single fruit lesion and completed in tissues or of citrus. many days to do that. one day (N.A. Peres, et al, Plant Dis - L.W. Timmer is with the University of Sweet orange scab can easily be ease, in press). Most of this work was Florida’s Citrus Research and Education confused with common citrus scab conducted in Brazil by N.A. Peres Center in Lake Alfred; N.A. Peres is with since the symptoms are very similar. working as a postdoctoral fellow on a the University of Florida’s Gulf Coast Re - The presence of scab symptoms on project funded by the California Cit - search and Education Center in Wimauma. sweet orange fruit is not sufficient to rus Research Board. J.W. Hyun is with the Korea Rural Devel - conclude that the disease is caused by No PCR or other molecular proce - opment Administration, National Institute E. australis . The state has one patho - dures were available for distinguish - of Subtropical Agriculture, Jeju, Korea.

CITRUS INDUSTRY • February 2007