Blushed pear research in Australia

Dr Ian Goodwin is the research leader for crop physiology at the Agriculture Victoria SmartFarm in Tatura. Fresh Quarterly spoke with him about their work on blushed pears. By Anna Mouton.

Q. How important are blushed cultivars to the Australian pear industry?

A. The total production of blushed pears is small compared with Williams’ and Packham’s, but we do grow a lot of Corella, which is similar to Forelle, in Australia. About 90% of our pears are grown in the area where I’m based — the Goulburn Valley — and there are still many traditional pear orchards in this part of the world.

These orchards are widely spaced — maybe 6 x 6 metres — and all vase systems. Some of them would be over a hundred years old. The only innovation that’s been done is converting to micro-irrigation.

But interest in blushed and fully red pears is definitely growing. One reason is that they will attract consumers to eat pears.

Corella was a parent of both the blushed pear cultivars that are branded in Australia. One is called Lanya [cultivar ANP-0118] and the other is Ricó [cultivar ANP-0131].

There are other cultivars that have been grown. One that was planted a lot around here is called Piqa Boo [cultivar PremP009]. It’s a fully red pear from the New Zealand breeding programme. Most of their releases have been interspecific selections — Asian-European pear crosses.

Our growers are very disappointed with it because it doesn’t become the bright red that you’ll see when it’s growing in New Zealand — it tends to brown. The obvious differences between here and New Zealand are that it’s much hotter here, and we’re in a higher light environment.

Q. What is the Profitable Pears project?

A. We started looking at some of the blushed pear cultivars that were bred in Australia. We put in an experimental orchard at our research station nine years ago and the name of the project was Profitable Pears. It was partly funded by the industry as well as by the Victorian government.

A second project was subsequently funded. That’s finishing in less than 12 months from now. We’re looking at a third project that will probably focus on colour development. We haven’t got it nailed in terms of what practices growers could use to get that maximum colour.

For example, we looked at the dynamics of how a blush pear becomes green when it is shaded and becomes red again when re-exposed. That seems to occur throughout the year but when getting closer to harvest, the green fruit can’t catch up in colour to a control.

So, in terms of management, we thought that it’s about summer pruning to expose fruit to more radiation, to get better colour, and maybe even using reflective mulch to try to stimulate colour development. But when we tried those things in practice, the results were not as obvious as in the controlled experiments.

We still don’t understand what’s going on there. My hypothesis is that there may be precursors in pears that are critical to starting anthocyanin synthesis and expression — these precursors might be critical at the very start of the season. We don’t know.

Q. Is protective netting used on blushed pears?

A. Netting in this part of the world was originally put up above apples for hail protection and subsequently provided enormous benefits in preventing sunburn damage. Packham’s and Williams’ do get sunburnt from excessive radiation in Australia, but netting is not used in our pears because the returns can’t justify the investment.

But if blush cultivars start to be grown more widely, I think the industry would net them because the fruit would be worth a lot more than Packham’s and Williams’.

We did some work looking at different netting shade factors. Even at a 20%–30% shade factor, which is pretty standard for apples, you were getting a loss of colour.

Q. What is the relationship between rootstocks and red colour?

A. There’s a really strong relationship between vigour, light, and colour. We can’t attribute it purely to the rootstock, but the restriction in vigour has a profound effect on light and therefore colour development.

The same goes for crop load. When we’ve compared a high crop load with a low crop load, there is much more vegetative growth in pears with the low crop load and therefore less colour. It seems to be just caused by shading.

In the Goulburn Valley, we have pretty heavy soil, so the dominant rootstock is D6 [a Pyrus calleryana clonal rootstock]. If you tried growing pears on D6 in Europe they’d be out of control — they’d be huge trees.

Our growers have always been concerned that without D6 the trees won’t have enough vigour. But our research has definitely shown that there’s no problem with vigour using quince rootstocks.

It would be great to have more dwarfing-type rootstocks like they have in apples. But in Australia, we’ve been laggards in importing pear rootstocks.

Q. What is next for research on colour development in pears?

A. There is now pretty good technology to measure the colour of the fruit in situ. And I think that’s going to speed up how we determine what is going on with respect to colour.

We can now take optical images with a mobile vehicle. We then use artificial intelligence to identify the fruit and measure its colour. We can even estimate colour coverage.

So, we can drive up and down rows very rapidly, take these images, process them, and get a measure of colour. For example, we can generate a spatial map of colour coverage in an orchard. I think being able to measure lots and lots of fruit is really valuable.

The next step to that is using LiDAR [3-D laser scanning] to recreate the actual tree as a digital image and to locate the fruit within that tree. We can use the fruit position to know how much light might hit that fruit, and we can synchronise that information with the colour measurement.

I think we’ve got huge opportunities to speed up the data collection and analysis that we use to look at the relationships between colour development and environmental factors.

Image: Dr Ian Goodwin demonstrates a multileader system for the blushed Ricó [cultivar ANP-0131] pear.

Supplied by Ian Goodwin.