Gustavo Mora-Aguilera

Enzymatic Activity and Pathogenicity of Entomopathogenic Fungi from Central and Southeastern Mexico to Diaphorina citri (Hemiptera: Psyllidae)

Abstract. n To understand the relationship between pathogenicity and enzymatic activity of fungal isolates associated with Diaphorina citri Kuwayama, three isolates of Beauveria bassiana (Bals.) Vuill. and six of Hirsutella citriformis Speare from southeastern and Central Mexico were characterized enzymatically. Pathogenicity against D. citri was evaluated in four of them. They killed >90%, and no differences among isolates were found; however, by the change rate (rL) of the logistic model, a trend of more mortality (1.12) was confirmed in the Bb-Ch isolate of B. bassiana obtained from adult D. citri from Quintana Roo State, while the Y-2 isolate of H. citriformis from Yucatan State resulted in least mortality (0.74). Enzymatic production, both intra and inter-specific, varied, but greatest variability was found in proteases, and there were strains without proteolytic activity. A positive relationship (r = 0.84 to 0.98) was found only between intracellular proteases versus pathogenicity; isolates with more and least production were Bb-Ch (3.15) and Y-2 (0.12), respectively, suggesting this methodology for detecting enzymes might be useful in selecting the most pathogenic isolates. Based on pathogenicity and intracellular enzymatic activity, strains with the greatest potential for managing D. citri were Bb-Ch and Bb-Cat of B. bassiana. Based on enzymatic activity only, Y- 5 and Camp-1 could be the H. citriformis strains more pathogenic to D. citri.

Agronomical management influence on the spatiotemporal progress of strawberry dry wilt in Michoacan, Mexico

The spatiotemporal distribution of strawberry wilt, caused by Fusarium oxysporum, Phytophthora sp., Pythium aphanidermatum and Rhizoctonia fragariae, was studied with the aim to establish the effect of some technological components of the strawberry crop cv. Camarosa (Fragaria x ananassa Duch.) and sustain their use in an integral management of the disease. Epidemics were characterized in two cropping seasons at three localities in Valle de Zamora, Michoacan, Mexico, in commercial plantations with plastic mulch and drip irrigation (A+G), and non-mulch and gravity irrigation (T) on a 100 m2 area per site. Temporal parameters were contrasting between both management techniques. A+G plantations had significantly lower final incidence (Yf =12.8±5.6%) than T (22.5±5.9%) (p=0.05) and were consistent with estimators of area of curve (ABCPEa and ABCPEe). The range of epidemic intensity reduction induced by A+G was 22.21 to 76.7% day, which was reflected in lower apparent infection rates (b-1=0.0015-0.0027, R2=0.92-0.99). Lloyd’s Index of Patchiness and Morisita Index (1.01 to 1.17) indicated a slightly aggregated dispersion pattern. Autocorrelation and geostatistical analysis confirmed lower aggregates in A+G (up to 5 plants) vs. T (8 plants), but an apparent higher mobility of inoculum in A+G up to 6.5 m. Plastic mulch and drip irrigation are proposed as technological components of an eventual integrated management program of dry wilt in Michoacan. n n xa0 n n Key words: Epidemiology, plastic mulch, drip irrigation, strawberry dry wilt.

Evaluación de barreras vegetales en el manejo integrado de la mancha anular del papayo (PRSV-P) en Michoacán, México

The effect of plant barriers as a component of an integrated management program (IM) was validated and adapted in 1999, in Michoacan, Mexico, to control papaya ringspot, caused by papaya ringspot potyvirus type-P (PRSV-P). A split-plot design was established with two experimental factors: plant barriers and components of IM: IM without oil sprinkling (IM-O), IM without plant rouging (IM-R), and complete IM. Plant barriers (Hibiscus sabdariffa), sowed 20 days before papaya transplanting, and plant rouging delayed the epidemics onset in 19 days thus IM resulted in the highest yield (14.2%) than the rest of the treatments, but it was less effective than IM-O in vigor (4% in stem diameter). Oil sprinkling was phytotoxic and caused a 5.3% vigor reduction. The oil effect on the disease progress was not clear, since the epidemic intensity (epidemic onset X0 = 47 days after transplanting, final incidence Yf = 81% and area under disease progress curve ABCPE = 3220 %days) was similar to the control treatment. Plant barriers alone may not be sufficient to reduce disease incidence and spreading. The more abundant winged aphids known as PRSV-P vectors were Aphis gossypii, A. nerii, A. spiraecola and Macrosiphum euphorbia, which represented approximately 13% of the total captured aphids.

Epidemiology of Entomopathogens: Basis for Rational Use of Microbial Control of Insects

Abstract. n Epidemiological studies are important for successful use of entomopathogens for pest management. Although microbial control of insects is applied epidemiology, there are few epidemiological-ecological studies, which partially explains why the use of entomopathogens has ended in failure. Isolated studies using preserved strains of entomopathogens in a laboratory might contribute to lack of efficacy under field conditions. An option is regional exploration of entomopathogens as the basis for epidemiological diagnoses, because this would enable identifying the most prevalent species and isolates that presumably have greater potential for use in pest management. Field epidemiological/ecological diagnoses allow identifying factors that induce the development of epidemics, including the range of hosts, plants, and cropping systems. Understanding their prevalence, dispersal, and pathogenicity is key to successfully detect pathogens in the field. Basic epidemiological characterization includes measuring n-variables associated with different categories or factors which as a whole explain the intensity of an epidemic (epidemiological system). Although epidemiology of entomopathogens has been studied in different regions of the world, variability (species and strains) and differing weather conditions make local epidemiological studies necessary. An agroecosystem for citrus production is a good model for epidemiological studies of entomopathogens. Fungi and phytosanitary diagnoses have been studied on citrus in the Yucatán Peninsula, Mexico. Future field studies, complemented with laboratory studies including characterization of pathogenic, physiological, and cultural aspect, with new methodological analytical approaches (i.e., Logistic and Weibull models), will aid rational use of entomopathogens in the field.

Virulence of Seven Isolates of Pandora neoaphidis 1 on the Cabbage Aphid Brevicoryne brassicae 2

Abstract. n During 2006, laboratory studies were conducted to evaluate the pathogenicity of seven isolates of Pandora neoaphidis (Remaudière & Hennebert) against the cabbage aphid, Brevicoryne brassicae (L.). Two isolates were obtained from the aphids Rhopalosiphum padi (L.) (TEXRP1), and Myzus persicae (Sulzer) (TEXMP1), infesting broccoli (Brassica napus (L.)) in Texcoco, Mexico; the rest of the isolates were obtained from Rhopalosiphum maidis (Fitch) infesting sorghum (Sorghum bicolor (L.) Moench), in five localities in Tamaulipas, Mexico. The greatest percentages of mortality were caused by isolates RBF, TEXRP1, y RBB, at a rate of 87, 76, y 72%, respectively, 240 hours after the initiation of the treatments. These results show the potential of P. neoaphidis as an agent of biological control against B. brassicae, depending of the place and the origin of the isolate.

Sample size for assessment of cladode brown spot in prickly pear cactus

Cladode brown spot (CBS) is an important disease of prickly pear cactus (Nopalea cochenillifera) in Brazil. No standard method exists for sampling in the field. A study was conducted in 30 fields of prickly pear (cv. Miúda) in Pernambuco state, Brazil, to determine the optimal sample size to assess severity of CBS. In each field, a 0.3xa0ha (45xa0×xa068xa0m) test area consisting of 30 rows and 45 plants per row (1350 plants per test area) was arbitrarily chosen. In each test area, 50 plants were sampled using a systematic method and the disease severity was assessed with the aid of a standard area diagram set on 2, 4 and 6 cladodes/plant. The spatial pattern of the disease was examined by spatial autocorrelation analysis and the optimal sample sizes were determined based on three levels of error (5, 10 and 20%). CBS severity in the fields ranged from 0.4 to 8.7%. In 15 fields the disease severity of CBS was >4.0% and in 20 fields the spatial pattern of CBS was aggregated. There was a positive correlation (rxa0=xa00.59, Pxa0=xa00.0001) between disease severity and strength of aggregation, and a negative correlation (rxa0=xa0−0.39; Pxa0=xa00.0001) between disease severity and sample size (number of plants). There was no significant effect (Pxa0=xa00.3) of the number of cladodes assessed per plant (2, 4 or 6 cladodes) on sample size. Considering a sample of two cladodes per plant and an acceptable error of 5, 10 or 20%, the optimal sample size was 253, 63 and 16 plants, respectively, for each 0.3xa0ha of cultivated field.