First approach to pod dehiscence in faba bean: genetic and histological analyses

Pod dehiscence causes important yield losses in cultivated crops and therefore has been a key trait strongly selected against in crop domestication. In spite of the growing knowledge on the genetic basis of dehiscence in different crops, no information is available so far for faba bean. Here we conduct the first comprehensive study for faba bean pod dehiscence by combining, linkage mapping, comparative genomics, QTL analysis and histological examination of mature pods. Mapping of dehiscence-related genes revealed conservation of syntenic blocks among different legumes. Three QTLs were identified in faba bean chromosomes II, IV and VI, although none of them was stable across years. Histological analysis supports the convergent phenotypic evolution previously reported in cereals and related legume species but revealed a more complex pattern in faba bean. Contrary to common bean and soybean, the faba bean dehiscence zone appears to show functional equivalence to that described in crucifers. The lignified wall fiber layer, which is absent in the paucijuga primitive line Vf27, or less lignified and vacuolated in other dehiscent lines, appears to act as the major force triggering pod dehiscence in this species. While our findings, provide new insight into the mechanisms underlying faba bean dehiscence, full understanding of the molecular bases will require further studies combining precise phenotyping with genomic analysis.

SEEDS, PODS AND PETIOLE GLAND’S CHARACTERISTICS OF LEUCAENA SPP. ANALYTICAL STUDY (A)

Twenty-two species were extracted from the Leucaena Spp. Data were collected on their characteristics, which differed from each other and were classified accordingly. Statistical analysis revealed that there were many differences between species in some traits; each type is itself in other qualities. Therefore, we presented the qualities that need to be described in order to identify differences. The study included the qualities related to seeds, pods and petiole gland. The seeds were aligned in Pods in three forms, while the shape of the seed came in two types. Only two types of species differed in the status of the opening of the pod (dehiscence). As for the thickness of the wall of the Pods, the species varied greatly, and the highest was the Papery. The rate of openness of the Pods was very high at 90.9% for one margin. The partitioning between seeds within Pods did not register more than two types, and it tended to have no partition by 72.7%. Only two shapes were distinguished in terms of the clarity of the seed chamber on the surface of the pods and 16 times the uncertainty was repeated ( not partitioned ) , leaving 6 replicates of the possible type of clarity ( partitioned ) . The colors of Pods differed very much, and each type had its own color except for some exceptions. The most frequent color was (To Orange Brown) with five replicates and the color (Mid Orange Brown) four times and the remaining types remained independent of colors. There was a high correlation between seed and pods traits and in some cases reached 90% at the probability of 1%. The length of the seed ranged between 4.9 mm - 10.6 mm but distributed over all types of tree under study. Each seed type had a specific seed length. The correlation coefficient between seed width and seed length was high at a probability of 1% to 0.775. Seeds / Kg was varied even within one species and was between 8700 - 70000 seeds / kg. There were only two forms that showed the accompaniment of the gland on the throat while three forms of the gland type were recorded but the gland height had a variety of forms.

Genetic Control and Geo-Climate Adaptation of Pod Dehiscence Provide Novel Insights into Soybean Domestication

Loss of pod dehiscence was a key step in soybean [Glycine max (L.) Merr.] domestication. Genome-wide association analysis for soybean shattering identified loci harboring Pdh1, NST1A and SHAT1-5. Pairwise epistatic interactions were observed, and the dehiscent Pdh1 overcomes resistance conferred by NST1A or SHAT1-5 locus. Further candidate gene association analysis identified a nonsense mutation in NST1A associated with pod dehiscence. Geographic analysis showed that in Northeast China (NEC), indehiscence at both Pdh1 and NST1A were required in cultivated soybean, while indehiscent Pdh1 alone is capable of preventing shattering in Huang-Huai-Hai (HHH) valleys. Indehiscent Pdh1 allele was only identified in wild soybean (Glycine soja L.) accession from HHH valleys suggesting that it may have originated in this region. No specific indehiscence was required in Southern China. Geo-climatic investigation revealed strong correlation between relative humidity and frequency of indehiscent Pdh1 across China. This study demonstrates that epistatic interaction between Pdh1 and NST1A fulfills a pivotal role in determining the level of resistance against pod dehiscence, and humidity shapes the distribution of indehiscent alleles. Our results give further evidence to the hypothesis that HHH valleys was at least one of the origin centers of cultivated soybean.

Physiological and molecular aspects of pod shattering resistance in crops

Pod shattering resistance is a trait acquired by crops in the process of evolution. Manipulation of physiological and molecular processes is fundamental for the improvement of shattering resistance in crops. In this review we discuss several enzymes, key hormones and their possible roles or relationships involved in pod shattering, and highlight responsible genes, quantitative traits loci (QTLs) and their implications for increased pod shattering resistance. Cell wall degrading enzymes, particularly β-glucanases and endopolygalacturonases play an important role in the process of pod dehiscence. It is not clear how and to what extent a specific hormone regulates the dehiscence zone differentiation and the dehiscence process is not clear. Resistance to shattering is highly heritable and is not controlled by a single gene. Several QTLs associated to dehiscence have been identified in crops, while the underlying genetic functions of these QTLs deserve further investigation. Further physiological analyses of the pod wall will help to understand better the pod dehiscence.

Genetic control of pod dehiscence in domesticated common bean: Associations with range expansion and local aridity conditions

SignificancePlant domestication has radically modified crop morphology and development. Nevertheless, many crops continue to display some atavistic characteristics that were advantageous to their wild ancestors, such as pod dehiscence (PD). Domesticated common bean (Phaseolus vulgaris), a nutritional staple for millions of people globally, shows considerable variation in PD. Here, we identified multiple genetic regions controlling PD in common bean grown throughout geographically distributed lineages. For example, on chromosome Pv03, PvPdh1 shows a single base-pair substitution that is strongly associated with decreased PD and expansion of the crop into northern Mexico, where the arid conditions promote PD. The environmental dependency and genetic redundancy explain the maintenance of atavistic traits under domestication. Knowledge of PD genetics will assist in developing aridity-adapted varieties.AbstractA reduction in pod dehiscence (PD) is an important part of the domestication syndrome in legumes, including common bean. Despite this, many modern dry bean varieties continue to suffer yield reductions due to dehiscence, an atavistic trait, which is particularly problematic in hot, dry environments. To date, the genetic control of this important trait has been only partially resolved. Using QTL mapping and GWAS, we identified major PD QTLs in dry beans on chromosomes Pv03, Pv05, Pv08, and Pv09, three of which had not been described previously. We further determined that the QTL on chromosome Pv03, which is strongly associated with PD in Middle American beans, includes a dirigent-like candidate gene orthologous to Pod dehiscence 1 (Pdh1) of soybean. In this gene, we identified a substitution in a highly conserved amino acid that is unique to PD-resistant varieties. This allele is associated with the expansion of Middle American domesticated common beans into the arid environments of northern Mexico, resulting in a high allelic frequency in the domesticated ecogeographic race Durango. The polygenic redundancy and environmental dependency of PD resistance may explain the maintenance of this atavistic characteristic after domestication. Use of these alleles in breeding will reduce yield losses in arid growing conditions, which are predicted to become more widespread in coming decades.