Kiwifruit pollination problems

Next time you eat a kiwifruit, cut it in half and look at it before taking a bite. Look for the little seeds – most kiwifruit have about 1,000, so you can’t miss them. To get seeds in a kiwifruit, a female flower must be pollinated – the more pollen it gets, the more seeds it produces. The more seeds it has, the bigger the fruit, so kiwifruit growers want all their crops to get heavily pollinated. Scientists such as Dr Mark Goodwin of Plant & Food Research are researching ways to help make sure kiwifruit plants get all the pollination they need.

Kiwifruit flowers are insect pollinated, but they are a bit unusual:

• The male and female parts are in separate flowers, which grow on separate plants. Insects need to collect pollen from male flowers and take it to female flowers for pollination to occur. Fruit are only formed by female flowers.

• Flowers do not have nectar to attract insects.

• Female flowers produce ‘fake’ pollen to attract insects. It is not the same as male pollen, because it does not contain genetic material or food.

The trouble with bees

For many years, kiwifruit growers have grown a few male plants amongst many female ones. They have brought beehives into their orchards so the bees can carry pollen from the male flowers to pollinate the female flowers. But recently, the bees haven’t been as successful as they used to. One of the main reasons is the varroa bee mite. This is a pest that spreads viruses that kill the bees. Even when varroa is controlled by chemicals, bee colonies are still weaker than they used to be. Another problem is that bees prefer many other flowers that grow around kiwifruit orchards, so visit them instead.

RoboBee

Many kiwifruit growers are turning to artificial pollination because bees have become unreliable pollinators. This involves collecting pollen by hand from male flowers and spreading it onto female flowers. Dr Mark Goodwin is carrying out research to help find the best ways to do this, including when to pollinate kiwifruit flowers and how much pollen to use.

One project he is involved in with Dr Paul Martinsen at Plant & Food Research is developing a new machine called RoboBee. This can sense where female flowers are on a vine and spray pollen directly on to them. Normally, pollen is sprayed all over a vine using a hand sprayer or machine, so a lot is wasted when it lands on leaves. Collecting and processing male pollen is very expensive, so the RoboBee will save a lot of pollen wastage.

Mark also studies the pollination of new varieties of kiwifruit that have been developed. Growers need to know when these new varieties flower, how long they flower for and how much pollen needs to reach a female flower for it to produce suitable fruit. The results of this research mean that growers will know how many bees they need or how much pollen they will need to spray on and how often they need to spray it.