Scientists are unlocking the secrets of water efficient faba beans

Roughly one-third of the world’s arable land is subject to water shortage, and with climate change expanding this area, farmers need more drought-adapted crops. Mandour and colleagues have brought farmers one step closer to drought-resistant faba beans by identifying genetic markers associated with water use efficiency in experiments published in Annals of Botany.  

Faba bean is a highly adaptable, productive, nutritious pulse with a long tradition of old-world cultivation. Two faba bean varieties known to have relatively high water use efficiency were used to create a population of recombinant inbred lines (RILs). RILs are genetically very similar plants developed by crossing two inbred parents and then self-fertilising the progeny over successive generations to create genetically distinct lines in a similar genetic background. This breeding scheme results in closely related plants that can be experimentally exploited to identify genes contributing to complex genetic traits.

In this case, the botanists identified genes associated with water transpiration rate. Transpiration is the amount of water taken up by a plant’s roots that then evaporates from its leaves. Plants regulate transpiration by opening and closing microscopic pores called stomata that are on the leaf surface. Water lost from leaves must constantly be replaced by water from the soil, leading to interest in improved transpiration rates as part of drought-resistance breeding programmes.

Using the RIL strategy, Mandour and colleagues identified genes associated with transpiration that could prove useful for water conservation. Plant transpiration was measured at six sequentially decreasing humidity levels by changing the ratio of dry to humid air within a whole plant gas exchange chamber. DNA was then isolated from the 165 RILs and their parental lines, and genotypic data was generated using a DNA array. A linkage map, which statistically links a trait such as transpiration response to a gene or genetic marker, was created to identify quantitative trait loci (QTLs). QTLs are genomic regions statistically associated with a physical (i.e., height) or physiological (i.e., drought tolerance) response. They are identified by measuring a trait such as transpiration rate and then statistically identifying a genetic region that is common across RILs presenting that trait.

Thirteen QTLs associated with transpiration rate were identified. The QTLs mapped to chromosomes 1, 3 and 5, and most of the QTLs are in or near genes known to regulate plant responses to abiotic stress. Even better, with the newly published faba bean genome, these genes of interest can be rapidly studied for their contribution to transpiration rate and can be used as part of a marker-assisted breeding programme. Ultimately, the identification of these genes can lead to faba bean varieties that more efficiently regulate their transpiration rate in arid conditions. If plants can be more efficient with their water supply, then they will be better equipped to tackle dryer conditions.

READ THE ARTICLE
Hend Mandour, Hamid Khazaei, Frederick L Stoddard, Ian C Dodd, Identifying physiological and genetic determinants of faba bean transpiration response to evaporative demand, Annals of Botany, Volume 131, Issue 3, 16 February 2023, Pages 533–544, https://doi.org/10.1093/aob/mcad006.