Resistance of rice genotypes to stem borers has been little studied in Brazil and worldwide. Studies involving resistance in rice to stem borer species have focused mainly on: D. saccharalis, an important pest in the Western Hemisphere and parts of South America, Central America, the Caribbean region and the Southern United States (Joyce et al. 2014, Reagan and Mulcahy 2019). Chilo suppressalis (Walker) (Lepidoptera: Crambidae) an important species of rice stem borer in Asia, the Middle East and Southern Europe (Jiang et al. 2015) and Scirpophaga incertulas (Walker, 1863) (Lepidoptera: Pyralidae) pest of economic importance in Asia (Ali et al. 2020). The study involving E. lignosellus in rice, are focused on seed treatment and chemical control (Ferreira and Barrigossi 2003) and cultural management (Ferreira and Czepack 1997). However, studies involving rice resistance to E. lignosellus are scarce and involve old cultivars (Ferreira et al. 1998).
The results showed the different behavior of E. lignosellus in rice cultivars, making it possible to establish different levels of resistance between the cultivars. Canela de Ferro, Nenenzinho, Progresso and Miúdo Branco presented the highest total stem number and Canela de Ferro, Lageado Ligeiro, IRGA 417, Nenenzinho, Guarani, Esmeralda, Pepita, Primavera, IAC 1278, Confiança and Bonança the lowest percentage of damaged stem. Rice plants with a greater number of stems suggest tolerance, due to a greater amount of biomass or emission of vegetative structures, being able to withstand or recover after pest infestation (Baldin et al. 2019, Almeida et al. 2021). Thus, the greater tillering capacity of rice plants, the lower damage was caused by E. lignosellus (Ferreira et al. 1979). The cultivar Canela de Ferro has already been demonstrated in other studies to be resistant to rice pests. Correa et al. (2018) demonstrated antibiosis/antixenosis in Canela de Ferro to D. saccharalis. Almeida et al. (2020) observed antibiosis/antixenosis in the cultivar Canela de Ferro to the rice stalk stink bug Tibraca limbativentris (Stål) (Hemiptera: Pentatomidae).
The damage caused by the larvae penetrating in the stem and plant consuming tissue forms the symptom known as “dead heart” (Barrigossi and Martins 2015). Plants of Canela de Ferro, Esmeralda, IRGA 417, Primavera, Miúdo Branco, Lajeado Ligeiro, Nenenzinho, Guarani, Pepita and Confiança showed the lowest proportions of “dead heart” symptoms. This lesser visualization of this symptom may be related to the greater hardness and lignification of the stem tissue of these cultivars.
Some of these cultivars also showed greater stem hardness, such as Primavera and Esmeralda, among 21 rice cultivars for resistance to T. limbativentris (Almeida et al. 2020). Another morphological characteristic that may be associated with a lower percentage of “dead heart” symptoms, is the silicon (Si) content, which provides rigidity in the plant tissue. The Si content was higher in the cultivars Esmeralda and IRGA 429, compared to Canela de Ferro, in a study of induction of resistance in rice cultivar to T. limbativentris (França et al. 2018).
These same cultivars also provided the lowest values for the number of live larvae, larval weight and larval length, except the cultivars Miúdo Branco, Nenenzinho and Guarani. These rice cultivars were shown to be unfavorable to the development of E. lignosellus larvae. The presence of amylase inhibitors, (Marsaro Júnior et al. 2005), Si content (França et al. 2018), low protein content (Arnason et al. 1993, Cunha et al. 1999) and stem sclerotization (Chaudhary et al. 1984), can confer resistance in rice plants to rice stem borer species. Van and Guan (1959) observed high larval mortality of Chillo suppressalis (Walker) (Lepidoptera: Pyralidae) in genotypes of Oryzae ridleyi (Hooka), due to the high sclerotization of the stem of these plants.
The rice cultivars that provided the worst performance for E. lignosellus presented the lowest incidence of damage. The cultivars IAC 1278, Xingu, Bonança, Guarani and Bico Ganga showed the greatest damage extent, while the other cultivars had the smallest extent. The causes of resistance in rice cultivars to pests that damage the stem are associated with chemical characteristics (França et al. 2018, Pelosi et al. 2022); morphological (Correa et al. 2018) and physical (Almeida et al. 2020). Nascimento and Barrigossi (2014) observed in rice cultivars with an external diameter greater than 2.5 mm susceptibility to D. saccharalis.
The UPGMA grouping method grouped susceptible cultivars into groups I and III and IV highly susceptible cultivars and the resistant group II, respectively. The cultivar with moderate resistance to E. lignosellus showed promise for use as a tactic in an IPM program by rice producers in Brazil or in a breeding program aimed at resistance to the stem borers (Smith 2005, Seifi et al. 2013).
The cultivar Canela de Ferro has already been classified as resistant to D. saccharalis in other studies (Nascimento and Barrigossi 2014, Nascimento et al. 2015, Correa et al. 2018, Pelosi et al. 2023) due to the narrow stem diameters. Ferreira et al. (2000) observed tolerance in Bonança and Carisma, due to the greater number of tillers and higher grain yield quality after D. saccharalis infestation. Pelosi et al. (2023) also observed tolerance in the genotypes BRS Formoso, Canela de Ferro, IAC 1278, IAC 899, IR 20, and IR 44 to D. saccharalis.
The rice cultivar Canela de Ferro showed resistance to E. lignosellus and can be used in rice breeding programs as a source of resistance to rice stem borers. Furthermore, the identification of rice genotypes resistant to E. lignosellus benefits rice producers, increasing crop productivity and reducing the use of insecticides to control the pests. Future studies need to be implemented to evaluate the levels and types of resistance involved in rice cultivars to lesser cornstalk borer and study interactions with other control methods in IPM of E. lignosellus.