TE, HE, UE and PHE variables have values comparable to those published in previous studies for the species (Silva et al. 2018). However, the lower TE number in G11051 could indicate some factor limiting oviposition in this genotype and could constitute a resistance mechanism different from the antibiosis reported in the literature (Jiménez et al. 2017). This behavior is of great interest given that Z. subfasciatus, females lay their eggs on the seed testa which influences the quality of stored grain.
Lower oviposition on seed was previously noted when evaluating common bean genotypes in free-choice trials (Filho et al. 2016, Guzzo et al. 2018). However, in trials without free choice the same results were not found, as genotypes were equally oviposited. In general, only the antibiotic resistance to Z. subfasciatus of some P. vulgaris wild genotypes and other genotypes of P. acutifolius is emphasized (Chrispeels y Raikhel. 1991, Prado et al. 2011; Tigist et al. 2017, Guzzo et al. 2018) and little emphasis has been placed on the possible mechanisms involved in adult repellency by seeds of some genotypes.
According to Jiménez et al. (2017), antixenosis in seeds plays a very important role as a resistance mechanism as this is the first resistance barrier controlling insects in the field or in storage.
The use of genotype G11051 in resistance improvement of P. vulgaris can play a substantial role. Therefore, it is of great importance to deepen the knowledge of the physical and chemical factors involved that may promote the lower preference of Z. subfasciatus to oviposit on the seeds of this genotype.
Accession G11051 presents very small seeds as is characteristic of the wild accessions used in the study (Cardona et al. 1990). However, Guzzo et al. (2015) did not detect correlations between the level of resistance and 18 morphoagronomic characters that included seed characters such as: mass of 1000 seeds, primary color, brightness, shape, number of colors, seed thread color, size and profile.
Jiménez et al. (2017, 2020) identified two new cultivars of tepary bean (P. acutifolius) that manifested new mechanisms of resistance to A. obtectus, including inhibition of oviposition and antixenosis in adults (assessed as insect percentage that did not approach the seeds over a period of time).
These mechanisms could be influencing the interaction of Z. subfasciatus females and accession G11051, so it is necessary to identify the mechanism that influences the lower oviposition and to study the inheritance type in order to use it in genetic breeding.
The susceptibility of commercial cultivars in Cuba constitutes a vulnerable aspect for the Z. subfasciatus management under storage conditions. These cultivars are currently used in bean production in the country. The absence of resistance in these cultivars, the deficit of inputs for the implementation of adequate management strategies for this pest, as well as the limited access that farmers manifest to the necessary materials to implement pest management strategies (Rodríguez et al. 2019), can raise infestation levels in storage and facilitates the rapid development of insects and the consequent losses in the volumes and quality of stored grain.
The low number of emerged adults in RAZ lines and wild accessions evaluated in these studies can be explained by the high mortality of larvae inside seeds due to the existence of antibiosis mechanisms related to the presence of arcelin variants as previously reported (Cardona et al. 1990, 1992). Such mechanisms limit the normal development of the larvae and cause high death rates. This results in a decrease in the emergence of adult insects, as well as a prolongation of the life cycle as observed in this study.
In the selection of RAZ lines, the most effective arcelin variants for Z. subfasciatus control were introduced. According to Cardona et al. (1990) these variants were in decreasing order: Arc1. Arc2 and Arc5 since the rest of the arcelin variants detected up to that time did not show high levels of resistance when introduced into susceptible varieties
Among the wild accessions are genotypes with arc3 and arc4 alleles, which do not confer high degrees of resistance to the insect. In this regard, in previous studies it was found that wild accessions containing Arc3 showed the lowest degrees of resistance when subjected to the insect (Cardona et al. 1990). Arc4 also did not confer high degrees of resistance in new breeded lines, so the introduction of these two variants was discarded from the breeding program.
The behavior detected in genotypes RAZ 36 and G11051-25-1-2 (Absence of emerged adults) shows the potential of the two materials for genetic breeding as donor progenitors of resistance genes to Z. subfasciatus.
On the other hand, it must have other factors that potentiate or diminish resistance, since some genotypes with the same arcelin variant show different behavior, according to the classification by scales, before the insect. Posso et al. (1989) found that the arcelin concentration is a determinant of the antibiotic effect on the insect. These same authors reported a significant prolongation in the adult emergence time of Z. subfasciatus as the concentration increased in artificial seeds with increasing levels of seed meal of the resistant genotypes G12866 and G12949, but at the same time, a greater effect of genotype G12949 was recorded than at concentrations higher than 60%, did not allow adult emergence. This suggests the need of searching for correlations with traits of interest in their seeds or other possible mechanisms involved in the resistance/susceptibility of these different lines and accessions.
Obtaining commercial cultivars with resistance to Z. subfasciatus represents an additional protection within an integrated pest management system in the crop (Boiça et al. 2021). These materials can be used with other alternatives within a pest control strategy due to their compatibility with other tactics, which contributes to reduce losses caused in storage conditions (Wanjiru et al. 2011).
Obtaining the order of resistance conferred by the different variants of arcelin
The order of resistance obtained in this work is in disagreement with that reported by Cardona et al. (1990), since these authors reported Arc5 as the variant that confers the highest resistance degree to Z. subfasciatus followed by Arc4, Arc1 and Arc2. Arc1 and Arc2. These same authors agree with these results, in that genotypes with Arc3, introduced in commercial cultivars did not show resistance. Acosta-Gallegos et al. (1998) when evaluating wild accessions they obtained the order Arc5 > Arc1 > Arc7 > Arc4 > Arc2 > Arc6 > Arc3. These researchers used one wild accession for each arcelin variant, with the exception of the Arc7 variant which was represented by three accessions. They also identified that accession G24582 (with Arc7) manifested a higher degree of resistance than accessions containing Arc1, although when averaged across the three sources, Arc7 came in third place.
The existence of divergence in the resistance degrees conferred by the different arcelin variants may be due to the number of materials analyzed by different authors in the studies. For example, Cardona et al. (1990) only evaluated one P. vulgaris wild accession of each arcelin variant. However, when using breeded materials (RAZ lines), these same authors found that those containing Arc1 showed the highest degree of resistance, those with Arc2 showed intermediate resistance and did not detect resistance in lines from crosses with Arc3 and Arc4 as a source of resistance.
With these results it is possible to design strategies for the exploitation of arcelin sources in breeding programs where it is desired to incorporate resistance to Z. subfasciatus. The use of breeded RAZ lines for this trait will contribute to save time in the identification of new resistant genotypes, since they do not possess the undesired traits of wild parents (Cardona et al. 1990).
There are no use reports of Arc7 sources in improving resistance to Z. subfasciatus. The results of this study showed that this variant confers a high degree of resistance, as do the variants Arc1. Arc2 and Arc5 (Cardona et al. 1990). It is suggested that genotypes showing Arc7 (G24582 and G24584) could be evaluated for introduction in breeding, which would increase the sources of resistance in these programs.
Analysis of the relationship between the resistance level to Z. subfasciatus and the nutrient content (Fe and Zn) of seeds
To date, the relationship between resistance to Z. subfasciatus and seed mineral content has not been studied. This result is of great importance if it is taken into account that in the new approaches to bean breeding programs, one of the main aspects is to obtain genotypes with higher Fe and Zn content (Diaz et al. 2022), which can contribute to the reduction of malnutrition in regions where the bean is highly consumed (Tofiño-Rivera et al. 2016). Since there is no relationship between resistance and Fe and Zn contents in seeds, it is possible to work on breeding and obtaining new cultivars resistant to Z. subfasciatus and with high content of these minerals.