Future proofing our pastures against drought

By Lynley Hargreaves 11/02/2015


Minushika Punchihewa
Minushika Punchihewa

New Zealand may have escaped another official declaration of drought, but climate-change forecasts make dry periods more likely. Good news, then, that a New Zealand high school student has helped improve the drought-resistance of future pastures. Former Palmerston North Girls’ High School student Minushika Punchihewa explains her Gold CREST research that ensures successful cross-breeding just by looking closely at a clover plant.  

Why are clovers being cross-bred?

Currently Trifolium repens (White Clover) is the most common species of clover used in New Zealand’s agricultural sector and is depended upon by farmers to feed their live stock and for pastoral growth. However, a relativity new type of clover called Trifolium ambiguum was introduced to New Zealand from regions surrounding the Black Sea. This clover has many advantageous traits such as drought tolerance, pest and disease resistance and strong rhizomes for spreading, so scientists are beginning to cross breed this clover with T.repens to try incorporate some of these beneficial traits.

Will new varieties be out in the paddock any time soon?

Scientists are always working to cross breed between various species of clover with Trifolium repens in order to find hybrids which have the most benefit to New Zealand’s agriculture. I am sure there are new varieties that are being used commercially in New Zealand, in particular through the research conducted by AgResearch.

The problem that arises from crossing T.ambiguum and T.repens, however, is that T.ambiguum can be found with different numbers of sets of chromosomes in the nucleus of the cell. If you cross diploid (two sets) or hexaploid (six sets) T.ambiguum  with the only tetraploid (four sets) T.repens you can get plants with odd ploidy. Due to their low fertility, these hybrids are useless for plant breeding programmes. It’s very important that scientists know the ploidy of T.ambiguum plants being used in breeding programmes. I looked into ways to figure out the ploidy of plants without having to resort to time-consuming or expensive laboratory techniques.

What did you find?

During the course of my research, I investigated a number of morphological traits from various stages of  plant growth. These included seed measurements, leaflet measurements, leaf markings and floral measurements. Results from these concluded that three major traits (seed size, red fleck and banner petal length) are useful for differentiating between diploid, tetraploid and hexaploid cultivars of Trifolium ambiguum. The traits observed cover different stages of a plant life cycle, so T.ambiguum ploidy can be determined in the seed, during the plant growth and flowering. This means that plant breeders can preferentially select particular seed, cull unwanted plants at the seedling stage or select individual plants during pollination, as a result saving a significant amount of time, money and resources.

What advice would you give students wanting to do a Gold CREST project?

Gold CREST is an incredible opportunity and a chance for students to expand their interest in a chosen field of science or technology. My advice for students would be that you get out of it in the end what you put into it; therefore it is crucial that every aspect during the planning, practical and writing up of the report is done thoroughly. Don’t be afraid to ask for help, as this is all part of the CREST process. It’s about finding the right balance between team work with mentors and independent thinking and understanding. It’s knowing that sometimes experiments may not always go as expected, but finding an innovative and creative method of reasoning is an important part of the process.

What would you like to work on in future?

Though I will not be pursuing a career in plant sciences, I am still extremely interested in this field and in the genetics of clover. This year I will be studying a bachelor of Health Sciences at the University of Auckland with the aim of getting into medicine.

CREST is an international awards scheme designed to encourage years 0-13 students to be innovative, creative, and to problem solve in science, technology and environmental studies.

These interviews are supported by the Royal Society of New Zealand, which promotes, invests in and celebrates excellence in people and ideas, for the benefit of all New Zealanders.