This article appeared in the Fall 2013 issue of Pulse Crop News.

Alberta chickpea growers have seen declining seed quality and yield over the past five years, and the plants’ indeterminate growth habits seem to be one of the major causes, according to Dr. Manjula Bandara, Special Crop Research Scientist at CDC South in Brooks.

“Chickpeas grow continuously, even after flowering, depending on weather conditions,” says Dr. Bandara. “In periods of high rainfall, chickpeas start regrowing late in the season instead of reaching maturity, and the resources intended for the earlier seeds are instead consumed by that regrowth. As a result, we get immature green seed, which reduces overall seed quality and marketable yield.”

To prevent this unwanted regrowth, chickpea breeders have been working on producing determinate varieties, with limited success so far. As a result, researchers such as Dr. Bandara have been exploring alternative agronomy practices as a possible solution – namely, the use of plant growth regulators to control the secondary growth habits.

Used successfully in Europe on winter and spring wheat crops for over 60 years, plant growth regulators are synthetic chemicals that suppress plant growth, in theory reducing the effects of secondary growth. With that in mind, Dr. Bandara and his research team began a three-year study in 2010 that explored the use of plant growth regulators on Kabuli chickpea crops.

“Our main objective was to look at secondary growth – how secondary growth affects seed quality, how plant height can be used as an indicator for secondary growth, and how plant growth regulators affect yield quality,” says Dr. Bandara.

To that end, Dr. Bandara’s research team set out to determine the best production practices for using plant growth regulators on chickpeas: application stage; concentrations; varieties; interaction with fungicides; and optimal conditions for use.

Using CDC Frontier – a medium-seeded and CDC Orion – large- seeded Kabuli type – as the test variety, Dr. Bandara set up one test site in Bow Island and another in Brooks. The intent was to maintain two separate irrigated and rain-fed sites in Brooks and an irrigated site in Bow Island, but moisture levels in 2010-11 were high as a result of heavy rainfall. Because of this, Dr. Bandara was able to maintain around 50 per cent moisture levels until flowering in Bow Island without the use of irrigation.

Three plant growth regulators – Cycocel, Apogee, and Palisade – were applied at four different concentrations at three growth stages: 10 days after flowering, 20 days after flowering, and 30 days after flowering. The research team wanted to have the flowers established prior to spraying, according to Dr. Bandara.

“We really didn’t have any idea how the chemicals would affect the flowering,” Dr. Bandara explained. “In some cases, we’ve found when you spray at flowering, it increases flower abortion, and we wanted to avoid that.”

The team also looked at different methods of applying the plant growth regulators. “In one case, we applied the chemicals alongside the fungicide. In another, we applied it separately. We wanted to see if there were any interactions between the chemicals, and we found there’s no difference on the activities when applied a fungicide, such as Headline® or Proline® and plant growth regulator together or separately.”

After three years of data collections at the two sites, Dr. Bandara’s research team concluded the study with some “unexpected results.”

“Based on the information we gathered over the last three years, the use of these chemicals on chickpeas under extreme conditions has no significant beneficial impact on seed yield improvement or maturity,” said Dr. Bandara.

Spraying with Cycocel resulted in no plant height reduction, and while both Apogee and Palisade reduced plant height for several weeks, the effect was temporary, and regrowth occurred before the end of the growing season. And while Cycocel did not harm the yield, both Apogee and Palisade at high concentrations produced lower yields.

Why this is happened is “uncertain,” according to Dr. Bandara. “The effect was inconsistent, but overall, there was no yield improvement.”

Though the study did not produce the desired results, Dr. Bandara feels that even negative results are important.

“In most situations,we ignore and do not report negative or neutral results,” said Dr. Bandara. “But now at least we know that, under these circumstances, using these compounds won’t be beneficial.”

Demand remains from lentil and chickpea growers to see if other plant growth regulators could be used to control secondary growth in these crops. Dr. Bandara feels that further research into the effects of plant growth regulators on pulses is needed.in Our current studies were conducted with a single application of plant growth regulators at a wide range of concentrations at different growth stages. In future studies, we may need to consider and test multiple applications of plant growth regulators at very low concentrations by tank mixing with fungicides.

“Research into using plant growth regulators is not new, but the crops that we’re dealing with are new and very challenging,” said Dr. Bandara. “We’re still far behind on breeding determinate types of lentils and chickpeas, so we have to figure out other solutions. We now know what doesn’t work, and further research will hopefully show us what does.”

This project was supported through funding under the Canadian Agricultural Adaptation Program (CAAP). In Alberta, CAAP is administered by the Agriculture and Food Council.