RESUMEN
This study aimed to determine whether foliar sprays of potassium silicate (KSi), sodium molybdate (NaMo), or a combination of both (KSi + NaMo), with or without the fungicide azoxystrobin (Azox), could reduce anthracnose symptoms and, consequently increase yield. Two two-by-four factorial experiments, consisting of untreated or fungicide treated, as well as sprays of KSi, NaMo, KSi + NaMo, and no spray (control), were arranged in a randomized block design with three replications. Treatments were as follows: treatment 1, KSi spray; treatment 2, NaMo spray; treatment 3, KSi + NaMo spray; treatment 4, Azox spray; treatment 5, Azox + KSi spray; treatment 6, Azox + NaMo spray, treatment 7, Azox + KSi + NaMo spray; and treatment 8, control (no KSi, NaMo, or Azox). The KSi, NaMo, and Azox treatments were sprayed at the rates of 35 g/liter, 90 g/ha, and 120 g a.i./ha, respectively. The KSi was applied at 20, 27, 40, and 55 days after sowing (das). The NaMo was sprayed only at 27 das whereas the fungicide was sprayed at 27, 40, and 55 das. Plants were inoculated with Colletotrichum lindemuthianum at 23 das. Azox reduced the mean area under disease progress curve (AUDPC) by 63% and mean yield was increased by 150%. Similarly, the mean AUDPC was reduced by 29, 14, and 41% with KSi, NaMo, and KSi + NaMo sprays, respectively, while mean yield increased by 13, 20, and 47%, with KSi, NaMo, or KSi + NaMo sprays, respectively. The variables leaf area index (LAI), leaf area index duration (LAD), healthy leaf area duration (HAD), and radiation intercepted (RI) were not affected by KSi spray. The values for the variables LAI, healthy leaf area index (HLAI), LAD, HAD, RI, intercepted radiation of the healthy leaf area, and healthy leaf area absorption were significantly increased as a result of NaMo spray. The results of the present study support the novel possibility of using a foliar spray of KSi in association with NaMo to decrease anthracnose symptoms in bean plants and, consequently, achieve greater yield.
RESUMEN
There are more than 300 blackberry (Rubus) species worldwide. Rubus brasiliensis Mart. is a native Brazilian species found in tropical forests. In January 2009, samples of R. brasiliensis with severe leaf blight were collected from an area of rain forest in the city of São Miguel do Anta, State of Minas Gerais, Brazil. Dark spots began developing in the young leaves and progressed to necrotic spots with occasional twig dieback. From the spots, a fungus was isolated with the following morphology: acervuli that were 20 to 50.0 × 50 to 125.0 µm and hyaline amerospores that were ellipsoid and fusiform and 7.5 to 23.75 × 2.5 to 5.0 µm. On the basis of these morphological characteristics, the fungus was identified as Colletotrichum acutatum. In Brazil, C. acutatum is reported in apple, citrus, strawberry, peach, plum, nectarine, olive, medlar, and yerba-mate, but it was not reported as the causal agent of leaf blight in R. brasiliensis. A sample was deposited in the herbarium at the Universidade Federal de Viçosa, Minas Gerais, Brazil (VIC 31210). One representative isolate, OLP 571, was used for pathogenicity testing and molecular studies. Identity was confirmed by amplifying the internal transcribed spacer (ITS) regions of the ribosomal RNA with primers ITS4 (3), CaInt2 (a specific primer for C. acutatum [2]) and CgInt (a specific primer for C. gloeosporioides [1]). Isolates of C. acutatum (DAR78874 and DAR78876) and C. gloeosporioides (DAR78875) obtained from Australian olive trees were used as positive controls. The primers ITS4 and CaInt2 amplified a single DNA product of 500 bp expected for C. acutatum. OLP 571 was grown for 7 days on potato dextrose agar. Young leaves of R. brasiliensis were inoculated with a conidial suspension (106 conidia/ml) on young leaves. Inoculated plants were maintained in a moist chamber for 2 days and subsequently in a greenhouse at 25°C. Necrotic spots similar to those described were detected on young leaves 3 days after the inoculation. Control leaves, on which only water was sprayed, remained healthy. The same fungus was reisolated from the inoculated symptomatic tissues. To our knowledge, this is the first report of C. acutatum causing leaf blight in the native species of R. brasiliensis in Brazil. References: (1) P. R. Mills et al. FEMS Microbiol. Lett. 98:137, 1999. (2) S. Sreenivasaprasad et al. Plant Pathol. 45:650, 1996. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.
