Breeding trends in vegetable brassicas

Seven key characteristics of crop improvement

The objectives of breeding programs can be broadly subdivided into two categories, namely ‘crop improvement’ and ‘product improvement’. ‘Crop improvement’ aims at addressing the needs of growers which include higher yields, stability of performance, disease-pest resistance, timely maturity, better response to applied inputs, etc. ‘Product improvement’ aims at meeting the needs of the consumer which involves complex quality characteristics like appearance, keeping quality, taste, flavor or nutritional value.

Traditionally, the crop improvement has received a top priority in the breeding programs. However, the breeding priorities vary from crop to crop and region to region depending on the specific requirements. In vegetable brassicas, the breeding objectives are more consumers driven and differ considerably from the standard pattern. Over time, an appropriate mix of product and crop improvement has emerged and is summarized as follows:

1. Crop Uniformity forms one of the most important objectives in the vegetable-breeding program. It was extremely difficult to achieve uniformity in crop growth and maturity with the open pollinated varieties. But with the development of F1 hybrids, much more uniformity in crop growth, maturity and produce quality, has become achievable. The availability of Cytoplasmic Male Sterility (CMS) lines in brassicas is further expected to help in producing F1 hybrids with better uniformity characteristics.

2. Produce appearance is another important breeding priority in vegetable brassicas. With the increasing role of packaging and display facilities in fresh produce marketing, the appearance plays a significant role. The fresh produce industry is always under pressure to produce good looking high quality vegetables, with appropriate size and shape, right color, firmness and good keeping quality. As most of these characters are complex in nature, the breeders have a herculean task to bring & keep them together.

3. High marketable yield is another significant objective because at the end of the day the growers need to produce and sell enough quantity, to be profitable. As the cost of production for a crop per unit of area, might nearly be the same, the crux of being profitable lies in achieving high marketable yields by intensifying efforts rather than spreading thinly over larger area. The varieties with better response to applied inputs and right characteristics are the centerpiece in this equation.

4. Disaese resistance is another important objective in vegetable breeding. The most important diseases which need emphasis in brassica breeding program are:

Downy mildew: Peronospora parasitica
Fusarium yellow: Fusarium oxysporum
Black rot: Xanthomonas compestris
Clubroot: Plasmodiophora brassicae

However, it is quite complicated and expensive to incorporate disease resistance into a commercially suitable variety. Therefore, in those situations where it is still possible to manage these diseases through cultural and chemical measures, the incorporation of resistance into the new varieties has not been that demanding. But with more and more emphasis on environmental issues, surge in organic farming, and tangible role they can play in IPM, the inbuilt disease resistance will become more important and is expected to take high priority in future.

5. Quality Characteristic incorporation is another important priority in the breeding program. This is keeping in line with the market requirements of developed countries and export markets, where the quality requirements are very stringent.

6. Improved Shelf life in fresh produce in general, is a very important feature of a variety which makes it stand or fall in the commercial sector. Even if the variety is performing very well in the fields, if the keeping quality is not good, it is very likely to fall out of favor of the marketplace managers. Better shelf life and keeping quality, therefore, makes another breeding objective.

7. Specific nutritional value: To large extent, vegetables are consumed for their health benefits. Breeding vegetable varieties with high level of natural substances having specific health benefit has fetched the breeders’ attention, rather of recent. One such glaring example is the Broccoli crop itself, which has a substance glucoraphanin with anti-cancerous activity. This has helped to increase its market share over the last decade tangibly. Knowing that this substance is controlled more by the genes rather than by the environment, it has become a separate breeding line. Similarly, breeding for higher levels of other natural substances like lycopene, flavonoids or antioxidants has become important aspects of vegetable breeding programs.

In general, with the availability of innovative techniques such as ‘double haploids/tissue

culture’ for producing homozygous parent lines, ‘Cytoplasmic male sterility’ (CMS) to facilitate cross-pollination in brassicas, and ‘DNA markers assisted selection’ for identifying the right genetic combinations, the breeders are much better equipped to address the field problems more effectively, pin pointedly, and in a shorter time.

As most of the major seed companies operate globally, the benefits of their breeding efforts become available instantaneously, around the globe. This is particularly relevant to the brassica varieties in New Zealand where most of the varieties are introduced at some stage from overseas, evaluated locally and the best ones are made available to the growers for cultivation.

The international breeding trends, therefore, have a direct bearing on our vegetable production sector. Most of the new varieties being introduced this year, not only have come out of this broad framework, but also aim at meeting specific needs of each crop, cropping niches and the local market requirements.

NOTE: This is an updated version of my article published in August 2001, in The Commercial Grower magazine.