Phaseolus lunatus landraces from northeast Brazil: genetic diversity and anthracnose resistance

Lima bean (Phaseolus lunatus L.) is an essential subsistence crop in Brazil, especially in the northeast, because of its adaptability to diverse environmental conditions and genetic variability. However, achieving high productivity remains challenging due to anthracnose caused by Colletotrichum truncatum. This study aimed to characterize the genetic diversity of Lima bean in Alagoas state and to identify anthracnose-resistant landraces. P. lunatus seeds were collected from local farmers in Alagoas between July 2017 and February 2018. Semi-structured interviews were conducted to examine the characteristics of Lima bean smallholders, focusing on socioeconomic, cultural, and agroecological factors. Genetic characterization of P. lunatus involved phylogenetic analysis of the internal transcribed spacer (ITS) region of ribosomal DNA and morphology analysis based on agronomic descriptors. The interviews confirmed that P. lunatus landraces were cultivated under rustic management conditions in subsistence agriculture. Twenty-seven landraces from twelve municipalities were obtained, representing three morphotypes: Big Lima, Potato, and Sieva, with Potato and Sieva being predominant. Lima bean landraces were classified genetically into Mesoamerican gene pools I and II, with the Big Lima morphotype grouped within the Mesoamerican gene pool II. Additionally, some hybrid landraces were identified. Broad resistance to anthracnose was associated with the Mesoamerican gene pool I, highlighting their importance for genetic improvement initiatives. This is crucial given the varied etiological agents of anthracnose across northeast Brazil.