Faba bean (Vicia faba L.) is an important cool-season legume crop that ranks fourth after chickpea (Cicer arietinum L.), field pea (Pisum sativum L.) and lentil (Lens culinaris L.) in terms of total production. The global production of faba bean was 4.8 Mt in 2017, with China, Ethiopia and Australia being the largest producers (1.8, 0.93 and 0.37 Mt, respectively). However, its area of production is not increasing relative to other crops, mainly because of high yield instability. This can be attributed to several factors related to plant traits (e.g. phenology, morpho-physiology) and biotic and abiotic stresses. Faba bean has a very poor flower : pod ratio, with a maximum 20% of flowers resulting in pods. Environmental stresses such as frost, heat and drought cause significant damage to flowers and young pods; therefore, matching phenology of crops to the environment is important for avoiding or minimising detrimental effects of unfavourable environmental conditions. In order to improve adaptation and yield, we need to understand the main factors affecting plant growth, including biotic stresses, identify the main yield components, and find traits associated with tolerance to frost, heat and drought.

Frost is one factor that causes extensive yield losses globally. A study was conducted to evaluate frost damage under field conditions and assess the genetic variation of flowers converting into pods. Diverse faba bean genotypes were evaluated under four growing seasons in a randomized complete block design: three at the University of Sydney, Narrabri, Australia (2014–2016) with three sowing dates, and one at the Agricultural Research Station, Dirab, Riyadh, Saudi Arabia (2016/2017) in one sowing. Visual methods were used to estimate frost damage and record the development of pods. Radiation frost in 2014 (Narrabri) damaged lower pods, while advection frost in 2016/2017 (Dirab) damaged upper pods. The radiation frost formed immediately above the ground; therefore, flowers and pods of taller plants minimized the damage because of their long distance from the ground. The earliest (mid-April) and middle sowing (7 May) suffered more by frost, while a delay in sowing (last week in May) led to frost escape or minor damage. The genotypes IX474/4-3 and 11NF010a-2 showed low sensitivity to frost at the vegetative and reproductive stages. Flowers developed at the beginning of flowering had a faster and higher pod formation rate (41–43%) than those formed later and contributed more to yields. Therefore, a severe frost at the beginning of flowering can cause a significant yield loss as these flowers are the most productive. The frost-tolerant genotypes, and faster and higher pod forming rates, identified in this study can be exploited to breed better varieties in the future.