Angus Stewart – horticulturist

This incredible diversity of Marguerite Daisies is part of an innovative breeding program at the University of Sydney’s Plant Breeding Institute at Cobbitty. These plants are sold by the millions around the world in places like Europe and North America. And the royalties that derive from them are a significant export earner for Australia. The reason this program is at the cutting edge is through the use of innovative breeding techniques like embryo culture.

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Angus Stewart – horticulturist

The earliest form of plant breeding was carried out by the first farmers who started to cultivate wild plants like this early form of tomato. Inevitably in every crop there were some seedlings that produced plants that had fruits that were a little bit bigger, mutations occurred in the genetic information of the wild plants and at the end we started to get these really massive fruits. So, it’s a technique that anyone can do by growing out a crop of seedlings you notice the biggest and the best you save the seed from those.

But then we progressed to a technique called cross-pollination where we wanted to incorporate the best features of two different plants. In most cases it’s two different species so there’s interspecific breeding. And a good example is the tomato. So, we’ve got a wild relative of the tomato and that has disease resistance characteristics for instance that we want to incorporate into the cultivated tomato.

So, to ensure that we get a cross-pollination of these two different genetic entities we first extract the pollen from the male parent, the wild relative of the tomato and we then remove the male parts of the female parent with a technique called emasculation. This ensures that we don’t get any chance pollination by insects. So, the pollen from the male parent is then transferred to the female part of the female parent and this pollen is rubbed onto the stigma, that pollen then germinates, grows down and fertilises the ovary and we get a hybrid fruit which then gives us a group of hybrid seedlings to select from.

Dr Nabil Ahmad – research fellow Sydney University

Well, tomato one of the major crops nowadays has been domesticated outside the centre of origin in South America for only a few hundred years. For me as a plant breeder the importance of the pro genetic diversity in tomato is actually to provide us with a very big gene pool that we use as plant breeders to improve the cultivated species.

So, now here we can see one species that’s originated in South America and this species has very, very invaluable genes that are used and have been exploited before for incorporating a resistance to insects and diseases in the cultivated tomatoes. But still it’s only the beginning. These species they have huge, huge pool of genes that can still be exploited and used in our breeding programs.

The obstacles that we face is that not all of the species, the wild species, not all of them can be actually crossed or hybridised with the cultivated tomatoes and that’s because some of them they have incompatibilities. So, as plant breeders we have the genetic or the molecular tools and the biotechnology tools that we use to overcomes these barriers, the incompatibilities. And we manage actually to hybridise these species with the cultivated ones. We rescue the embryos at one stage and we originate the plants that have been resulted from the cross between the cultivated and the wild ones.

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Angus Stewart – horticulturist

One of the really exciting developments in plant breeding has been the use of laboratory techniques and technologies that have dramatically expanded the range of possibilities for plant breeders.

For instance laboratory techniques in genetic analysis now enable us to pinpoint single genes and discover differences in those and enable those genes to be used for instance as markers in breeding programs which can greatly speed up the process and cut many years off a breeding program.

Plant tissue culture techniques have made all sorts of developments possible. For instance things like another culture and ovule culture enable us to secure genetically pure lines which can be used to greatly enhance the process of breeding genetically stable new varieties.

Things like somatic embryogenesis are used to take vegetative cells and by manipulating those we could get those to form embryos as they would with a zygote that has been produced by conventional pollination but by using those vegetative cells we can regenerate whole new plants and often create new genetic diversity which can also be used in conventional breeding programs.

One of my favourites is the technique of embryo rescue and the daisy breeding program here at the Plant Breeding Institute at Sydney University is using that technique to create intergeneric hybrids. These are hybrids that would not normally be possible by conventional breeding methods.

So, we take one genus of daisy hybridise that with another genus and then extract the tiny immature embryo, grow it in tissue culture on a sterile nutrient medium. It’s a bit like growing it on a humidicrib and that nurses the embryo through until it can form a plantlet which then can be grown on and planted in the greenhouse.

So, it’s opening up a whole new world of breeding possibilities to create hybrids that just weren’t possible even twenty years ago.

Dr Nabil Ahmad – research fellow Sydney University

In Australia there is more than twenty different species of the native tomatoes and these species actually they are endemic to the more driest area of Australia like central Australia, Northern Territory, Southern Australia and Western Australia.

We can exploit that gene pool by incorporating those genes into the cultivated tomatoes. The fruit of the bush tomatoes have been consumed by Aboriginal people for thousands of years. The fruits have been consumed fresh, dry and even they use them for flavouring their food.

Those tomato species usually have some incompatibility with the cultivated tomatoes so overcoming these incompatibilities is an important step to do that we have to study the breeding system of the plants.

We have to study the floral structure and biology to be able to find the compatibility and viability of the male and female parts. The wild tomato species they have dormancy in their seeds. The fruits are left on the plants to dry and that’s why they call them the desert raisin. Once the fruits are big the seeds can be extracted from the fruits. The seeds usually they have dormancy and that’s why we have to treat the tomatoes with special chemicals in order to overcome that dormancy and be able to germinate the seeds.

In our breeding techniques actually we use some biotechnology tools as I said to overcome some of the barriers, the incompatibility barriers but also sometimes we are interested in creating even more variability to get some desirable characteristics that are not available in nature. And we do that by using some tissue culture techniques. We also employ the use of marker assisted selections in our reading programs to speed up the programs efficiently, make use of time and space that is available to us.

Marker assisted selection is a very powerful tool that we use. We find some markers that are closely linked to some diseases, resistance or to some for instance abiotic stresses. By using those particular markers we actually can always be sure that the characteristic that we are interested in is always existing in our selection without even the need to grow the plants until maturity. So, we save on time. We save in effort and the cost as well.

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