Morpho-molecular identification and pathogenicity test on fungal parasites of guava root-knot nematode eggs in Lampung, Indonesia

Swibawa IG, Fitriana Y, Solikhin, Suharjo R, Susilo FX, Rani E, Haryani MS, Wardana RA. 2020. Morpho-molecular identification and pathogenicity test on fungal parasites of guava root-knot nematode eggs in Lampung, Indonesia. Biodiversitas 21: 1108-1115. This study aimed to obtain and discover the identity of the species of fungal egg parasites of root-knot nematodes (RKN), which have a high pathogenic ability causing major losses in vegetable crops. The exploration of the fungi was carried out in 2016 and 2018 from Crystal guava plantations in East Lampung, Central Lampung, Tanggamus, and NirAma, a commercial product that has been used for controlling Meloidogyne sp. in Indonesia. Identification was carried out based on morphological characteristics and molecular-based gene sequential analysis of Intergenic Transcribed Spacer (ITS) 1 and ITS 4. A pathogenicity test was carried out in vitro and in a greenhouse using tomato plants as indicator plants. In the in vitro test, observations were made on the percentage of infected RKN eggs. The observations in the greenhouse test were carried out on RKN populations in the soil and roots of tomato plants, root damage (root knots), and damage intensity due to RKN infection. The exploration resulted in five isolates of fungal egg parasites of RKN from the guava plantations in East Lampung (2), Central Lampung (1), Tanggamus (1), and from the isolation results of commercial products (1). The isolates were given codes as B4120X (PT GGP PG1), B3010 (PT GGP PG4), B412G (PT GGP PG 4), B01TG (Tanggamus), and BioP (Commercial products). Based on their morphological characteristics, the isolates were classified into the genus of Paecilomyces. The results of molecular identification showed that the discovered fungi were Purpureocillium lilacinum (Thom.) Luangsa Ard. (Syn. Paecilomyces lilacinus (Thom.) Samson.). Based on the in vitro tests, the five fungal isolates were able to parasitize RKN eggs at 86.4-100%. In the greenhouse test, all isolates significantly suppressed nematode populations in the soil and tomato roots, inhibited the formation of root knots, and produced lower damage intensity compared to controls. Among all the isolates tested, B01TG had the best ability to infect nematode eggs (99.5%), suppressing the formation of root knots, nematode population in the soil and the roots of tomato plants, and the damage intensity compared to other isolates.

Pathogenicity and virulence of entomopathogenic nematodes against Dichelops melacanthus Dallas (Hemiptera: Pentatomidae)

Infestations of Dichelops melacanthus (Dallas; Hemiptera: Pentatomidae) in corn and wheat in Brazil, and the subsequent damage, have increased in recent years, mainly owing to this insect’s ability to survive the off-season. The control of this insect is mainly carried out with chemical insecticides, but the development of alternative methods, such as biological control, can contribute to a more sustainable management. Thus, the objective of this study was to evaluate the potential of entomopathogenic nematodes (EPNs) for the control of D. melacanthus. A selection test was performed with 15 isolates of genera Steinernema and Heterorhabditis regarding their pathogenicity and virulence on adults of D. melacanthus. Concentration (10, 20, 40, 50, and 100 infective juveniles (IJs)/cm2) and greenhouse tests were carried out only with the Steinernema feltiae isolate (IBCB-n 47). All experiments were conducted in a completely randomized design. The selection test data were submitted to the Scott-Knott averages test (P ? 0.05), and those from the greenhouse test to the Student's t-test. The results of the concentration assay were subjected to regression analysis. All isolates showed pathogenicity and virulence in adults of D. melacanthus. The isolates GL (Heterorhabditis amazonensis), IBCB-n27 (Steinernema sp.), and RSC05 (H. amazonensis) were the most virulent (80.0, 82.0, and 88.0% mortality, respectively). The higher concentrations of S. feltiae (50 and 100 IJs/cm²) were responsible for the highest mortality rates of green belly stink bug (88.0 and 86.0%, respectively). In the greenhouse test, S. feltiae caused higher mortality (38%) than the control.

Inheritance of resistance to cotton blue disease

The objective of this work was to determine the inheritance of cotton blue disease resistance by cotton plants. Populations derived from the CD 401 and Delta Opal resistant varieties were evaluated, through a greenhouse test with artificial inoculation by viruliferous aphids. Cotton blue disease resistance is conditioned by one dominant gene, both in CD 401 and Delta Opal varieties.

The inheritance and durability of scab resistance in apple progenies

In order to select the appropriate parent cultivars and maintain the durability of resistance, it is important to clarify the mechanisms of inheritance of scab resistance depending on the parents. It has been known that the progeny segregation ratios based on scab-resistance do not depend only on the genotype of the resistance locus but also on the genetical makeup of the donor and recipient parents as well as on the susceptible parent. The aim of this study has been to demonstrate what factors in the Vf, Vr and VA scab-resistant cultivars — combined with susceptible and resistant parents — affect the inheritance and durability of resistance in seedlings in their first 4 year's growing four years' growth. After inoculating apple seedlings sown in 2001 with the suspension of Venturia inaequalis (Cke.) Wint. in the greenhouse, we studied the segregation ratios of the progenies into reaction classes. Seedlings showing resistance in the greenhouse were also evaluated for scab-resistance after they had been moved to the field and had naturally been infected with the pathogen in 2002 and 2004. The majority of our results obtained in the greenhouse test, similarly to earlier experiences, have not justified monogenic inheritance at the phenotypic level. The effect of susceptible parent cultivars on the segregation ratio of progenies have become apparent again. The high infection rate of seedlings in the field trials, which had previously exhibited varying degrees of resistance in the greenhouse test, has raised concern. Our data has raised further doubts, concerning the durability of Vf resistance in Hungary. It is assumed that the composition of natural field populations of Venturia inaequalis in Szigetcsép has changed. The complexity of Vf resistance has been confirmed. The high infection rate in the progenies derived from Vf resistant cultivars draws the attention to the importance of utilizing additional sources of resistance.

Screening Hybrid Citrus Rootstocks for Resistance to Tylenchulus semipenetrans Cobb

The response of 22 citrus hybrid rootstocks to a Mediterranean biotype of Tylenchulus semipenetrans Cobb was determined in a greenhouse test. Five of the 11 rootstocks with Poncirus trifoliata (L.) Raf in their parentage did not support nematode reproduction. However, rootstocks with Troyer citrange [Citrus sinensis (L.) Osbeck × P. trifoliata (L.) Raf] in their parentage were susceptible to the nematode.