ISSN 0100-2945 DOI: http://dx.doi.org /10.1590/0100-29452018005 Plant Protection Survival of Acidovorax citrulli in infected melon tissues and in different edafoclimatic conditions Aldenir de Oliveira Alves1, André da Silva Xavier2, Claudeana Souza da Conceição3, Rosa de Lima Ramos Mariano4, Elineide Barbosa de Souza5 Abstract- The survival of Acidovorax citrulli Aac1Rif was accessed in infected melon tissues (fruits and leaves) incorporated to the soil at 0, 5, 10 and 15 cm depth, in seven different types of soil, at temperatures 10, 15, 20, 25, 30 and 35 ºC and moisture field capacity of 50 and 100% in the absence of the host plant. Aac1Rif was detected in melon tissues at 0, 5 and 10 cm until 21 days and at 15 cm until 14 days. The highest and lowest relative extinction rate of the population (RERP) for Aac1Rif occurred respectively in fruit tissues and leaf tissues at depths of 0 and 5 cm. Aac1Rif survived in seven types of soil only for three days. The lowest RERP occurred at 10 or 15 ºC and the highest at 30 or 35 ºC. Greater concentrations of Na+, silt, and greater populations of actinomycetes and Trichoderma were correlated with highest RERP of the Aac1Rif in the soil. There was significant difference between RERP at 100% and 50% of field capacity. The soil was not considered potential primary source of A. citrulli inoculum. Infected melon fruits and leaves in soil were considered as such sources, at least for 21 days. Index terms: Cucumis melo, bacterial fruit blotch, populational density, ecology, management Sobrevivência de Acidovorax citrulli em tecidos infectados de melão e em diferentes condições edafoclimáticas Resumo - A sobrevivência de Acidovorax citrulli Aac1Rif foi estudada em tecidos infectados de frutos e folhas de melão incorporadas ao solo a 0; 5; 10 e 15 cm de profundidade, em sete diferentes tipos de solo, às temperaturas de 10; 15; 20; 25; 30 e 35 ºC e umidade na capacidade de campo de 50 e 100%, na ausência da planta hospedeira. Aac1Rif foi detectado em frutos de melão e tecidos foliares a 0; 5 e 10 cm até 21 dias, e a 15 cm até 14 dias. A taxa de extinção relativa mais alta e Corresponding author: mais baixa da população (TERP) para Aac1Rif ocorreu, respectivamente, nos tecidos de frutos e [email protected] nos tecidos foliares, às profundidades de 0 e 5 cm. Para a maioria dos solos, a TERP mais baixa + Received: Janeiro 17, 2018. ocorreu a 10 ou 15 ºC, e a mais alta, a 30 ou 35 ºC. Maiores concentrações de Na , silte e maiores Rif Accepted :May 17, 2018. populações de actinomicetos e Trichoderma foram correlacionadas com maior TERP de Aac1 Copyright: All the contents of this no solo. Houve diferença significativa entre a TERP em 100% e 50% da capacidade do campo. journal, except where otherwise O solo não foi considerado fonte primária potencial de inóculo de A. citrulli. Os frutos e folhas noted, is licensed under a Creative de melão infectados no solo foram considerados como fontes de inóculo, pelo menos por 21 dias. Commons Attribution License. Termos para indexação: Cucumis melo, mancha aquosa, densidade populacional, ecologia, manejo 1PhD in Phytopathology - Universidade Federal Rural de Pernambuco, Recife-PE. Brazil. E-mail: [email protected] 2PhD in Phytopathology. Professor at the Universidade Federal do Espírito Santo, Alegre-ES. Brazil. E-mail: [email protected] 3MSc in Phytopathology. PhD student at the Universidade Federal Rural de Pernambuco, Recife-PE. Brazil. Email: [email protected] 4PhD in Phytopathology. Professor at the Universidade Federal Rural de Pernambuco, Recife-PE. Brazil. E-mail:[email protected] 5PhD in Phytopathology. Professor at the Universidade Federal Rural de Pernambuco, Recife-PE. Brazil. E-mail: [email protected] 1 2 A. O. Alves et al Introduction Material and Methods Bacterial fruit blotch (BFB) is one of the most Bacterial strain destructive diseases in melon (Cucumis melo L.) and The A. citrulli spontaneous rifampicin-resistant watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) mutant (Aac1Rif) used in this study was obtained from on producing regions throughout the world (BURDMAN; the Culture Collection Rosa Mariano of the Laboratory WALCOTT, 2012). BFB is caused by Acidovorax citrulli of Plant Bacteriology, Federal Rural University of (Schaad et al.) Schaad et al. (Schaad et al., 2008) that Pernambuco, and was originally isolated from melon plant appears in the EPPO (European and Mediterranean Plant exhibiting typical BFB symptoms. The strain Aac1 (syn. Protection Organization) Alert List (CABI, 2015). In AAC201-21) belongs to the Group I of A. citrulli sensu Brazil, the most significant economic impact of BFB is on Walcott et al., which includes strains isolated mainly from melon crops (CARVALHO et al., 2013) mainly cultivated non-watermelon plants (WALCOTT et al., 2004). and exported in Ceará and Rio Grande do Norte. In these In previous studies, A. citrulli Aac1Rif showed states, BFB crop losses are estimated at 40-50%, but could growth in liquid culture medium and pathogenicity reach 100% (EPPO, 2013). similar to the rifampicin-sensitive parental strain (SILVA Seeds represent the most important source of et al., 2006). In all survival studies, A. citrulli Aac1Rif primary inoculum for BFB outbreaks. This confirms what was cultivated on nutrient yeast dextrose agar medium has been observed in field, that expanded leaves and stems (PUSEY; WILSON, 1984) amended with rifampicin at 1 are the main inoculum sources for melon blossoms and mg mL−1 (NYDARif); suspensions of mutant were prepared fruit (ALVES et al., 2010). Volunteer cucurbit seedlings, in distilled water and the optical density was adjusted noncucurbit and cucurbit weeds, and infected plant debris in a spectrophotometer model 500 M (Analyser) to A560 are also potential inoculum sources; however, these are not = 0.25, which corresponds to 3.4 x 107 colony forming important in all environments (BURDMAN; WALCOTT, units (CFU) mL-1. 2012). Developing better management practices depends on having knowledge of saprophytic dynamics of A. Survival of A. citrulli in infected melon tissues citrulli, but few studies were conducted on survival of the buried in the soil at different depths bacteria in crop residues and soil. A. citrulli survives in the To produce infected melon tissues, fruits and soil for a few weeks during the summer in the absence of leaves of yellow hybrid AF4945 were inoculated with watermelon plants (ISAKEIT, 1999). However, Silva et the A. citrulli Aac1Rif utilizing the sub-epidermal injection al. (2006) detected the decline of A. citrulli populations method (SOMODI et al., 1991) and atomization until run- 7 -1 over a 60-day period, from more than 10 cells mL to 10 off, respectively. Ten days after inoculation, symptomatic cells and to 100 cells, in rhizosphere soil and melon roots, fruits and leaves were collected separately and fragmented respectively. In crop residues, the bacterium has been into pieces of approximately 1 cm. Ten grams of tissue recovered from fragments of watermelon rinds buried at were individually placed in plastic mesh bags with 20 to 30 cm for 10 months (LATIN et al., 1995). openings of 2 x 2 mm and dimensions of 8 x 5 cm and The bacterial survival in soil is influenced by abiotic incorporated to the soil [pH in water = 5.1; P+= 6 mg (dm3)- factors such as temperature, moisture and pH (JANSE, 1; Na+ = 0.31 mg (dm-3) -1; K+ = 0.03 mg (dm-3)-1; Ca2+ + 2005) and depends on their ability to resist a lack of Mg2+ = 1.45 mg (dm-3)-1; Ca2+ = 0.9 mg (dm-3)-1; Al3+ = 0.25 nutrients and water, and exposure to heavy metals (GREY; mg (dm-3)-1; potential acidity (H + Al) = 5.2 mg (dm-3)-1; STECK, 2001; HASHIMOTO et al., 2006). None study organic C. = 11.52 mg (dm-3)-1; organic matter. = 19.86 mg were found about the influence of chemical and physical (dm-3)-1]. The bags were buried side by side at four depths characteristics of the soil on the survival of A. citrulli. [0 (surface), 5, 10 and 15 cm] in plastic columns of 20 Seed disinfestation treatments, seed health testing cm height x 10 cm diameter, containing 2 kg of soil, and and chemical control in the field are limited in their ability kept inside a greenhouse where the average air and soil to reduce the yield losses associated with BFB. In addition, temperature, and the relative humidity were monitored. to date, there are no reliable sources of BFB resistance The plastic columns were periodically wetted to maintain (BURDMAN; WALCOTT, 2012). A better comprehension the soil moisture close to the field capacity (90%). of the ecology of A. citrulli will contribute toward the The bags containing plant tissue were sampled development of BFB new management strategies. at 7-day intervals until two successive samples failed in This study aimed to analyze the survival of the detected A. citrulli Aac1Rif. Five bags per depth and type of bacterium (i) in fruit and leaf tissues incorporated in the infected tissue were collected in each sample. Following soil at different depths, and (ii) in different types of soil manual sample homogenization, 1 g from each bag was of the northeast region of Brazil in the absence of the host macerated. This macerated tissue was added to 9 mL of plant under the influence of different temperatures and sterilized distilled water (SDW) in tubes, and sonicated moisture levels. with an Ultra Sony™ 5B (Dentsply Neytech) for 5 min Rev. Bras. Frutic., Jaboticabal, 2018, v. 40, n. 5: (e-005) Survival of Acidovorax citrulli in infected melon tissues and in different edafoclimatic conditions 3 at 46 KHz.