Grains Research and Development

Date: 01.11.2001

Answer to black point: resistant varieties on horizon by Gary Alcorn

Top marks for black point wheat pathologist Miriam Michalowitz (left), barley scientist Maria Sulman and program leader Glen Fox as they prepare a critical BP extract for analysis.

AFTER seven years of innovative investigation, Peter Williamson and his colleagues at the Leslie Research Centre in Toowoomba, Queensland, have found evidence indicating the black point (BP) discolouration phenomenon on wheat and barley is climate-induced and not a fungal infection as generally accepted.

Growers can lose up to $50 million a year (ABARE estimates) in downgrading from export Prime Hard to feed or even total rejection as North Asian buyers, in particular, regard this discolouration as a disease indicator.

The team's research was part of the National Wheat Molecular Marker Program supported by graingrowers and the Federal Government through the GRDC. Both the Queensland Department of Pri mary Industries and the University of Southern Queensland's (USQ) Faculty of Sciences were also heavily committed to the program.

The good news is that, thanks to this collaboration, "We will definitely have a marker for black point resistance in Sunco types by the end of this year," says Dr Williamson. The challenge then is to incorporate a minimum level of 'resistance' in all new releases.

Dr Williamson stresses that the weather conditions that induce black point will also increase the levels of fungi in grain, causing previous researchers to blame fungi for the discolouration.

"My initial work showed there's an enzyme - peroxidase - occurring in grains tissue that becomes blackened. This enzyme causes browning in plant tissue when cells are damaged.

"We have been trying to identify the chemicals involved in wheat and barley BP and very recently discovered the precursors from which these compounds are formed; so we are getting close to unravelling the chemistry behind the discolouration.

"It's looking more and more like BP is not induced by fungi but by a reaction that occurs when there's moisture intake at that critical grain dry-down stage. In other words, it appears natural chemicals that are always in the grain combine and react during a prolonged moist ripening," he said.

Black point doesn 't harm germination, yield or quality. "The commercial value of grain is usually lowered to an extent out of proportion to the actual injury," Dr Williamson said. "In bread wheat, BP is thought to produce discoloured bran and wheat germ. Durum wheat products such as pasta assume a 'specky' appearance and are particularly unattractive.

"We are working with plant breeders to screen out highly susceptible types very early in evaluation trials so every future variety will have some level of resistance. There is no known immunity to the problem, which also occurs in most other grain," he said.

Program 2.2.1 Contact: Dr Peter Williamson 07 4639 8888 email WilliaP@prose.dpi.qld.gov.au

Region North