Tolerance of Caladium Cultivars Florida Cardinal and Florida Fantasy to Sulfonylurea Herbicides

There is a need to identify postemergence (POST) herbicides for weed control in field-grown caladium [Caladium bicolor (Aiton) Vent.]. The objective of this research was to evaluate the tolerance of two caladium cultivars Florida Cardinal and Florida Fantasy to POST applications of sulfonylurea (SU) herbicides flazasulfuron, foramsulfuron, imazosulfuron, and mesosulfuron. At 8 weeks after treatment (WAT), ‘Florida Cardinal’ and ‘Florida Fantasy’ treated with the highest rate of imazosulfuron (1680 g a.i./ha) had <10% visual injury, leaf number, height, and tuber weight reduction compared with the nontreated control. Both caladium cultivars exhibited greater susceptibility to flazasulfuron, foramsulfuron, and mesosulfuron as compared with imazosulfuron. The label-recommended rate of flazasulfuron (52 g a.i./ha), foramsulfuron (29 g a.i./ha), and mesosulfuron (15 g a.i./ha) reduced ‘Florida Cardinal’ height 35%, 27%, and 35%, respectively, and reduced ‘Florida Fantasy’ height 43%, 31%, and 21% compared with the nontreated plants, respectively. Caladium tuber weight exhibited a differential cultivar response to the evaluated SU herbicides, except imazosulfuron. The highest rate of flazasulfuron (420 g·ha−1), foramsulfuron (232 g·ha−1), and mesosulfuron (120 g·ha−1) reduced ‘Florida Cardinal’ tuber weight 50%, 65%, and 58% compared with the nontreated control, respectively, whereas these treatments reduced ‘Florida Fantasy’ tuber weight <25%. The mesosulfuron rate required for 20% tuber weight reduction (T20) in ‘Florida Cardinal’ was 2 g·ha−1, but the T20 value was 28 g·ha−1 for ‘Florida Fantasy’. We concluded that the caladium cultivars Florida Cardinal and Florida Fantasy are highly tolerant to the POST applications of imazosulfuron, whereas these caladium cultivars are more susceptible to flazasulfuron, foramsulfuron, and mesosulfuron.

Pathogenic Variation of Colletotrichum lindemuthianum causing Anthracnose of Beans (Phaseolus vulgaris) in Uganda

Colletotrichum lindemuthianum is a highly variable pathogen of common beans that easily overcomes resistance in cultivars bred with single-gene resistance. To determine pathogenic variability of the pathogen in Uganda, samples of common bean tissues with anthracnose symptoms were collected in eight districts of Uganda, namely Kabarole, Sironko, Mbale, Oyam, Lira, Kapchorwa, Maracha and Kisoro. 51 isolates sporulated successfully on Potato Dextrose Agar and Mathur’s media and were used to inoculate 12 differential cultivars under controlled conditions. Five plants per cultivar were inoculated with each isolate and then evaluated for their reaction using the 1 – 9 severity scale. Races were classified using the binary nomenclature system proposed by Pastor Corrales (1991). Variation due to cultivar and isolate effects was significant (P≤0.001) for severity. The 51 isolates from eight districts grouped into 27 different races. Sironko district had the highest number of races followed by Mbale and Kabarole. Races 2047 and 4095 were the most frequently found, each with 10 isolates grouped under them. Race 4095 was the most virulent since it caused a susceptible (S) reaction on all 12 differential cultivars and the susceptible check. This was followed by races 2479, 2047 and 2045 respectively. Two races, 4094 and 2479, caused a susceptible reaction on the differential cultivar G2333, which nevertheless, showed the most broad spectrum resistance followed by cultivars Cornell 49-242, TU, and AB136 respectively. These cultivars are recommended for use in breeding programs aiming at breeding for broad spectrum resistance to bean anthracnose in Uganda.

First Report of Resistance of Wheat Line Avocet ‘S’ to Stripe Rust Caused by Puccinia striiformis f. sp. tritici (Pst) in Syria

Seedling assays and field-based assessments are common approaches used in monitoring pathogenic variability of Puccinia striiformis f. sp. tritici (Pst). Due to the many candidate genes for resistance, and the occasional presence of uncharacterized or unexpected resistance genes, interpretation of seedling and adult plant responses of stripe rust differential genotypes can be confounded. To facilitate data interpretation and overcome growth habit differences, a set of near-isogenic lines (NILs) based on a susceptible selection of the widely susceptible Australian spring wheat cultivar Avocet was developed in Plant Breeding Institute, University of Sydney. During the 2011 rust survey of major wheat growing areas in Syria, we collected and recovered two isolates, one from bread wheat and one from durum, using susceptible cultivar Morocco. Fresh urediniospores collected from inoculated seedlings of cultivar Morocco under greenhouse conditions were used to infect a differential set of seedlings comprising the Avocet S NIL series with Yr1, 5, 6, 7, 8, 9, 10, 15, 17, 27, 32, A, SP and a supplementary set of Kalyansona (Yr2), Fielder (Yr6, Yr20), Thatcher (Yr7), Federation*4/Kavkaz (Yr9), TP1295 and TP981 (Yr25), Ciano 79 and Opata 85 (Yr27), Lemhi (Yr21), Anza (YrA), Tres/6*Avocet ‘S’, Cook, Avocet S, and Federation following standard protocol (1). Seedling infection types (IT) were recorded 15 to 17 days post-inoculation using a 0, ;(fleck), 1 to 4 scale, with ITs 3 and 4 considered to be high. According to European race nomenclature (1), these isolates would be classified as 6 E0 and assumes that differential cultivars Lee (Yr7) and Heines Kolben should be susceptible. A low infection of ;N (necrotic areas without sporulation) was observed on Avocet S and Avocet NILs Yr1, 5, 8, 10, 15, 17, 32, A, and SP. NILs Yr6, 7, and 9 responded with high infection types. Among the supplementary set, IT ;N was recorded for Anza, Cook, Tres/6*Avocet S, Opata 85, and Ciano 79 whereas IT 3+4 occurred on Kalyansona, Fielder, Thatcher, Federation*4/Kavkaz, TP1295 and TP981, and Lemhi. Federation and Morocco were susceptible to both isolates. Based on these data we concluded that 1) Avocet S carries at least one effective gene for resistance to the two isolates (temporarily designated as YrAvS and perhaps the same as the gene(s) in Anza and Cook); and 2) since Avocet S was resistant, it was expected that all the NILs should also be resistant unless one of the selected resistance genes was closely linked in repulsion with the gene in Avocet S. Since such a situation is possible for only one line, other explanations are that the recurrent parent, Avocet S, was not genetically homogeneous, or more likely, that the genetic background of Avocet S was not fully regenerated during the six backcross and subsequent selfing generations. This work illustrates the problems that can arise when sets of differential genotypes that perform in a satisfactory way in a particular (limited) geographical area are applied globally. Pst races carrying avirulence genes that are not present in the original area where a differential cultivar is characterized for its susceptibility may be present in other areas. Consequently, a differential cultivar which was susceptible in the original area may unexpectedly exhibit resistance in a new region. Therefore, host lines considered to be “universally susceptible” in one region may not be susceptible globally. The resistance of Avocet S is yet to be characterized. Reference: (1) R. Johnson et al. Trans. Br. Mycol. Soc. 58:475, 1972.

Incidence of Fusarium oxysporum f. sp. lycopersici Races in Tomato in Sinaloa, Mexico

Sinaloa State is the main producer of tomatoes (Solanum lycopersicum L) in Mexico where production attained 15,784 ha in 2008 (3). Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (Sacc) Snyder & Hansen causes significant yield losses in Sinaloa each year (2). Three pathotypes or races of F. oxysporum f. sp. lycopersici have been described: races 1, 2, and 3 (1). The purpose of this study was to determine the races of F. oxysporum f. sp. lycopersici present in Sinaloa and distribution of these races in the region. F. oxysporum f. sp. lycopersici isolates were obtained from plants showing symptoms of yellowing and necrosis of vascular bundles. Plants were sampled from 50 fields throughout the production area in Sinaloa from November 2008 to March 2009. Four differential cultivars were used to identify the races of 26 F. oxysporum f. sp. lycopersici isolates collected across Sinaloa: Bonny Best (susceptible to all races), UC-82-L (susceptible to races 2 and 3), F1 MH-1 (susceptible to race 3), and IR-3 (resistant to all races). A microconidial suspension was prepared for each isolate (1 × 106 CFU/ml) from cultures grown in potato dextrose broth with constant agitation (110 rpm) at 28°C for 7 days. Five 25-day-old seedlings (three fully expanded true leaves) from each differential cultivar were immersed in the appropriate microconidial suspension for 10 min, then individually transplanted into a pot containing 1 kg of sterilized commercial potting mix, and grown in a growth chamber at 25 to 28°C and 60 to 75% relative humidity for 5weeks with 14-h light/10-h darkness. Control plants (root dipped for 10 min in sterile water) were grown similarly and remained asymptomatic. Susceptible cv. Bonny Best showed typical symptoms of Fusarium wilt including epinasty, yellowing, defoliation, vascular necrosis, and wilt. None of these plants survived 25 days postinoculation for any of the isolates. All UC-82-L plants inoculated with each of the 26 isolates died before 35 days, indicating that none of the isolates was of race 1. F1 MH-1 plants only survived inoculation with 3 of the 26 isolates (11.5%), indicating that the 23 isolates that killed these plants (88.5% of the 26 isolates) were of race 3, and only 3 isolates were of race 2. All IR-3 plants inoculated with the 26 isolates survived. The isolates showed variation in response to the differential cultivar UC-82L in duration from inoculation to when the plants died (variation in isolate aggressiveness). The three F. oxysporum f. sp. lycopersici race 2 isolates were restricted to the Culiacan Valley, whereas the 23 F. oxysporum f. sp. lycopersici race 3 isolates were widely distributed across Sinaloa. Koch's postulates were confirmed by reisolating the fungus from the roots and stem base of each dead, inoculated plant (4). This study provides baseline data for future surveys to monitor changes in distribution of F. oxysporum f. sp. lycopersici races in Sinaloa, Mexico. References: (1) G. Cai et al. Phytopathology 93:1014, 2003. (2) P. Sánchez-Peña. Programa de Fomento y Apoyo a Proyectos de Investigación (PROFAPI), Universidad Autónoma de Sinaloa, México, 2007. (3) Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación, Servicio de Información Agroalimentaria y Pesquera, México. www.siap.gob.mx , 2009. (4) B. A. Summerell et al. Plant Dis. 87:117, 2003.

Identification and Distribution of Soybean mosaic virus Strains in Southern China

From 1,417 leaf samples with Soybean mosaic virus (SMV)-like symptoms collected from about 1,500 fields of 117 counties of 13 provinces in Southern China during 2004 to 2006, 201 SMV isolates were obtained after biological purification with single-lesion isolation and serological determination. Based on disease reactions on 10 differentials used in China as a representative from various reported differential cultivar systems, the isolates were grouped into 12 strains. Among them, eight were the same as those previously reported from Northeast China and the Huang-Huai Valleys while the other four were new and were designated as SC18, SC19, SC20, and SC21. Strains SC15 and SC18, which were predominant and widespread in Southern China, accounted for 32.3 and 26.4% of the total isolates and were distributed in 9 and 10 provinces, respectively. Thus far, 21 strains have been identified in the three soybean-producing regions in China under the uniform differentials system. According to their responses on the 10 differentials, the strains were clustered into five groups at similarity coefficient 0.6. Among them, SC15 in cluster V is the most virulent strain because it infects all differentials. Therefore, specific attention should be placed on control of its prevalence in soybean production.

Races and hosts of Pseudomonas syringae pv. tomato in Serbia

During the past few years, frequent appearance of bacterial speck of tomatoes was recorded in several tomato-growing regions in Serbia. A three-year survey of tomato fields in Serbia (2002-2004) resulted in the isolation of numerous bacterial strains, with 30 representative strains selected for further analyses. Based on the results of pathogenicity, biochemical, and physiological tests, all strains isolated from diseased tomato plants were identified as P. syringae pv. tomato. The identity of strains was confirmed by the polymerase chain reaction (PCR), since PCR products of expected size (650 bp) specific for coronatine-producing strains of P. syringae pv. tomato were amplified from all tested strains. Study of the host range of P. syringae pv. tomato strains originating from Serbia confirmed tomato as the sole host. The reaction of tomato differential cultivar Ontario 7710 showed that the Serbian strains belonged to races 0 and 1 of P. syringae pv. tomato.

Characterization of Colletotrichum lindemuthianum isolates using differential cultivars of common bean in Santa Catarina State, Brazil

In 2003 and 2004, 32 isolates of Colletotrichum lindemuthianum obtained from the infected plants of field-grown common bean (Phaseolus vulgaris L.) in Santa Catarina state, Brazil were analyzed based on the virulence to 12 differential cultivars of Phaseolus vulgaris L.. Thirteen distinct races were identified, six of which had not been reported previously in Santa Catarina. This is the first report of the occurrence of 67, 83,101,103,105, and 581 races of C. lindemuthianum. Race 65 was most common (34%). All the isolates were compatible to the cultivars Michelite and Mexico 222. Some isolates infected not only differential cultivar of Mesoamerican origin, but also the ones of Andean origin.

First Report of Race 8 of Downy Mildew, Caused by Peronospora farinosa f. sp. spinaciae, of Spinach in the United States

Downy mildew, caused by Peronospora farinosa f. sp. spinaciae, is the most economically important disease of spinach (Spinacia oleracea) in the United States and the European Union. In the United States, 23,000 ha of spinach, with a crop value of approximately $170 million, were grown during 2005 (1; http://www.nass.usda.gov/index.asp ). Additionally, per capita, fresh-market spinach consumption has increased 214% in the past decade (1; http://www.nass.usda.gov/index.asp ). Increased demand for fresh-market spinach has led to changes in spinach production practices such as higher planting densities and year-round production. There are currently 10 described races (races 1 to 10) of P. farinosa f. sp. spinaciae. Race 8 was recovered from the Netherlands in 2004 (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]), but has not been previously identified in the United States. In February 2007, several commercial fresh-market spinach fields in central Arizona were severely affected with downy mildew. Symptoms consisted of bright yellow leaf lesions ranging in size from 1 to 3 cm in diameter that supported dense purple sporulation of the pathogen on the corresponding abaxial leaf surface. Affected fields were primarily planted with spinach cv. Parrot, which is reported to be resistant to races 1 to 7 and 9. As much as 32 ha were affected and disease incidence reached as high as 25 to 30%. An isolate (PAR1) of the pathogen was obtained and used to inoculate a standard set of 10 differential spinach cultivars for race identification as previously described (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]). Briefly, a spore suspension (1 × 105 sporangia per ml) was misted onto test plants; plants were then incubated in a dew chamber (20°C, 100% relative humidity) for 24 h and maintained in a greenhouse. Inoculation tests were conducted at least twice at each of two different locations (Arkansas and California), with each test including two replications of 15 plants per differential cultivar. The selective development of downy mildew on specific differentials indicated that the isolate was race 8 (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]). To our knowledge, this is the first report of race 8 in the United States. Since there are a number of commercial spinach cultivars available with resistance to race 8, the economic impact of this race in the United States is expected to be low if resistant cultivars are grown (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]). Reference: (1) R. N. Acharya and I. Molina. NFAPP Newsl. Second Quarter, 2005.