Genetic Resources and Crop Evolution 47: 55–61, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 55 Diversity of boron-toxicity tolerance in lentil growth and yield Sui-Kwong Yau 1 & William Erskine 2 1 American University of Beirut, Faculty of Agricultural and Food Sciences, P.O. Box 11-236, Beirut, Lebanon; 2 The International Center for Agricultural Research in the Dry Areas (ICARDA), P.O. Box 5466, Aleppo, Syria Received 21 January 1999; accepted in revised form 8 April 1999 Key words: B-toxicity symptom, germplasm accessions, growth and yield, Lens culinaris Abstract Boron (B) toxicity is increasingly being recognized as a problem in arid areas of West Asia, where lentil is widely grown. This study investigated whether or not: (1) phenotypic variation of B-toxicity tolerance exists at the seedling stage in lentil, (2) such variation persists to affect adult performance, and (3) there is geographical diversity in seedling tolerance. Four experiments were conducted in a greenhouse. Boric acid was added and mixed uniformly into the soil-mix to prepare high-B soil. Experiment I screened 77 lentil lines randomly selected from ICARDA’s international nurseries. Visual growth scores and foliar B-toxicity symptom scores were taken 4–5 weeks after sowing, and used as an indicator for B-toxicity tolerance. In Experiments II and III, four selected lines were studied beyond the seedling stage. In Experiment IV, 231 lentil accessions from seven different countries/regions of the world were screened. There were highly significant differences between the 77 lines in B-toxicity tolerance at the seedling stage as indicated by their degree of B-toxicity symptom, and plant growth. The two tolerant and two sensitive selections from Experiment I showed diverse performance up to maturity as reflected by their differences in leaflet loss, dry mass reduction, and seed yield when grown in high-B soil. There were significant differences in B-toxicity tolerance between the 231 accessions. On average, accessions from Afghanistan were the most tolerant, followed by those from India, Iraq, Syria, Europe, Ethiopia, and Nepal. Introduction Boron (B) toxicity occurs mainly in arid areas (Kan- war & Randhawa, 1974), and has been reported in South Australia, India, Iraq, Pakistan, Peru, and USA (Nable, 1992). The Mediterranean region has above- average topsoil B levels (Sillanpaa, 1982). In West Asia and North Africa, B toxicity is increasingly being recognized as a problem (Yau et al., 1994). Barley (Hordeum vulgare L.) and lentil (Lens culinaris Medik.) are usually grown under rainfed conditions in dry areas in West Asia. Variation in B-toxicity tolerance in barley was associated with gen- otype by environment interaction in grain yield (Yau & Tahir, 1996). Working on wheat in dry areas of Australia, Holloway & Alston (1992) suggested that B-toxicity tolerance is needed for drought tolerance in high-B soils. In such environments lentil is a common component of cereal-based rotations. However, no information is available on the vari- ation in B-toxicity tolerance within lentil, except that lentil as a crop is less tolerant than barley to high soil B (Chauhan & Asthana, 1981; Singh & Singh, 1984). In contrast, many studies have been conducted in bar- ley, which has a large variation in B-toxicity tolerance (Nable, 1988; Paull et al., 1988; Yau et al., 1994). Genetic variation in response to high concentrations of B has also been reported in pea (Pisum sativum L.) and medics (Medicago spp.) (Paull et al., 1992). Information on variation in tolerance to B toxicity in lentil is needed to facilitate breeders in the region to initiate breeding for B-toxicity tolerance. The objectives of the study were to investigate whether or not: (1) phenotypic variation for B-toxicity tolerance exists at the seedling stage in lentil, (2) such variation persists to affect adult performance, and (3) there is geographical diversity in seedling tolerance.