The clearest outcome from a project examining field on seed mould and in-crop activities affecting faba bean production in South Australia is overwhelmingly in favour of growers planting newer PBA varieties “sooner than later”, according to SARDI researcher Dr Rohan Kimber.
He says the three-year trial showed that Fiesta and Farah had poorer seed quality and greater detrimental responses to agronomic practices compared with newer varieties, such as PBA Rana, PBA Samira and PBA Zahra.
Similarly, older varieties, such as Nura, were most susceptible to pod wall residue on seed, which could be confused with field mould, in some instances. This was found to be a hereditary trait, and the breeding program was selecting against this trait in newer varieties.
Dr Kimber said a high incidence of field mould in 2010 had triggered the ‘Mould of faba bean seed affecting seed quality and meeting export standards’ project, which found that variety had a significant effect on seed quality and the impact of in-crop practices.
He said mechanical damage caused by in-crop traffic reduced grain weight and increased staining, however this was mostly seen in Fiesta and would be minimised where growers use controlled traffic practices. Timely windrowing had no effect on seed quality, though late windrowing combined with late harvesting of windrow saw a significant reduction of quality in Fiesta beans where weather conditions were unfavourable. Crop topping had a significant effect on seed quality, with early crop topping before seed maturation increasing seed shrivelling and weather staining, and often diminishing uniform colour and size.
Field trials were performed in 2013, 2014 and 2015 at Bool Lagoon, Cockaleechie and Tarlee investigating the practices of crop topping, windrowing and the impact of wheel tracks. Grain quality was examined on harvested seed, including the total number of blemished seeds, colour tone, 100-grain weight, grain uniformity, weather-stained seed, shrivelled seed, ascochyta staining and pod-wall adhesions.
The core objectives of Dr Kimber’s team at SARDI, in conjunction with the University of Adelaide’s Faba Bean Breeding Program, were to determine the impact of crop management practices and varietal interaction of field mould and provide advice on distinguishing between symptoms.
“Optimal timing of windrowing, crop topping and timing is recommended, particularly in Fiesta, Farah and Nura, which were the most susceptible to these practices,” Dr Kimber said.
“Implementation of practices that reduce the impact of wheel tracks, such as controlled traffic farming, can prevent plants producing poor quality seed in wheel tracks.”
Growers adopting newer PBA types were being urged to avoid possible genetic drift by isolating them from other varieties, with at least a 200-metre buffer between paddocks, particularly as they bulk seed stocks for subsequent plantings.
Dr Kimber said it made economic sense for growers to make the switch to newer varieties.
“Growers who transition from planting Farah or Fiesta to new PBA varieties will be better placed to reduce inputs and get the best seed quality and the maximum dollar for their crops,” he said. This had also been aided by PBA’s objectives to deliver higher yielding varieties with improved resistance to ascochyta and chocolate spot.