Chickpeas, compared to other grain legume species, are highly vulnerable to cool or chilling temperatures, leading to substantial fluctuations in their yields. Winter conditions impede seedling growth, while mean daily temperatures below 15°C result in flower and pod abortion. Consequently, chilling tolerance has become a priority trait for Australian chickpea growers and breeding programs.

However, improving chilling tolerance is complex with two main hurdles impacting progress; limited genetic variation within elite germplasm; and the absence of reliable screening or phenotyping methods.

These issues are now being addressed the first thanks to a prior GRDC investment with CSIRO which identified chilling tolerance sources in wild chickpea species, originally from Turkey. Progress was made possible through trials conducted in both Turkey and Australia, culminating in the crossing of this genetic material with commercial lines and the development of elite chickpea populations.

To overcome the second hurdle, GRDC has invested in a one-year project to develop a reliable and efficient field-based method of phenotyping for use in pre-breeding and commercial applications with the Western Australian Department of Primary Industries and Regional Development (DPIRD). It aims to complement and strengthen phenotyping efforts at CSIRO.

By achieving these objectives, more-accurate identification and selection of chilling tolerance traits during pre-breeding activities can be realised, increasing the likelihood of these traits being adopted and selected through commercial breeding programs. Eventually, commercial chickpea varieties with these traits will be released to Australian growers.

Method development

Chickpeas are particularly susceptible to chilling temperatures during the flowering stage. At this critical stage, when either the pollen and/or the ovary are exposed to chilling temperatures, successful fertilisation is inhibited, leading to embryo abortion and compromised pod set.

In cases where fertilisation does occur, the embryo is still vulnerable to chilling temperatures, causing it to abort and leaving the pods empty and non-viable.  These are all factors that determine the pod viability, with a viable pod being one with all grain filled.

As pod viability is considered one of the most-important traits for chilling tolerance in chickpeas, a dependable field phenotyping methodology known as ‘pod marking’ based on this trait has been developed.

This is a simple method which involves the use of a paintbrush and a water-based, UV-resistant paint. Pods that set during the chilling period are dot-marked and, after four weeks of grain filling, they are harvested. This approach allows for the assessment of seed-bearing pods which were formed exclusively during the chilling period, and excludes pods that formed later outside this period. The chilling period is characterised by an average screen temperature below 13°C.

Findings

Using the phenotyping method, chickpea lines have been identified that flowered and set viable pods in chilling conditions from a set of 378 chickpea lines (that included breeding lines and commercial varieties).

The viability of pods varied significantly among different lines, ranging from 21 per cent to 97 per cent. Among the commercial lines there were no significant differences in pod viability. PBA Striker had the highest pod viability at 89 per cent, followed by PBA Drummond at 88 per cent and CBA Captain at 73 per cent.

Interestingly, there were 29 lines that exhibited slightly higher pod viability than PBA Striker . These were crosses between domesticated chickpea and wild species.

The wild chickpea species Cicer echinospermum and crosses between this species and commercial chickpeas (C. arietinum) were the top four lines with high pod viability. Generally, the Cicer arietinum-echinospermum hybrids displayed higher pod viability compared to a cross with another wild species, Cicer reticulatum.

The results indicate that chickpea hybrid 937-1-218 had the highest number of viable pods with a total of 121, followed by a cold-tolerant wild parent (Bari3_100) with 86 viable pods and Kayat_077 with 76 viable pods. Bari3_100 and Kayat_077 were both collected from the province of Mardin, Turkey. PBA Striker remains the highest among the commercial genotypes, with 68 viable pods.

937-1-218 is a hybrid between a cold-tolerant wild parent, Gunas_100, collected from the province of Diyarbakir in Turkey and the domesticated parent Kyabra , which is commercially available in Australia. The hybrid produces twice as many pods as the cultivar PBA Striker and 70 per cent of the set pods on the hybrid plant are still viable, which is a relatively high number compared to PBA Striker . Overall, it appears that 937-1-218 has some desirable traits, including high pod viability, and increased pod production, which could make it a valuable candidate for a future crossing program.

The chickpea chilling tolerance field trial site at Dale, Western Australia. Photo: Amanuel Bekuma

Further investigation into the specific chilling-tolerant traits present in these wild species and their subsequent crosses would be worthwhile.

By selecting and promoting lines with a greater proportion and number of viable pods, breeders and growers can enhance the overall resilience and productivity of crops in challenging environments.

A new GRDC investment will build on this recently concluded project. The new project will combine the field phenotyping approach and development of diagnostic molecular markers for chilling tolerance.

The project will also aim to develop high-throughput technique(s) to accelerate chilling tolerance screening in chickpeas. Collaborative expertise from DPIRD, CSIRO and Agriculture Victoria will be harnessed to speed up the delivery of chilling-tolerant germplasm to breeders and ultimately new varieties to growers.

More information: Dr Amanuel Bekuma, [email protected]; Dr Brenton Leske, [email protected]

The authors would like to acknowledge the Centre for Crop and Disease Management at Curtin University for generating the wild chickpea introgression lines used in the study, under GRDC investment CUR1406-001RTX. We also would like to acknowledge Dr Kefei Chen from Analytics for the Australian Grain Industry (AGGI) for statistical support, and Jens Burger, Dr Olive Onyemaobi, Jane Brownlee and Kelley Whisson from CSIRO for technical inputs. The project was supervised by Dr Darshan Sharma.