Citrus varieties hybridize fairly easily and many crosses are known, both natural and man-made. Commercial breeders look to develop new varieties that will increase profits through improved yield, better storage qualities, attractive appearance and sometimes even through new or tastier flavours.
There is another group of hybridizers, often amateur, whose goal is to produce a frost-hardy citrus plant with sweet, edible fruit. They usually start with Poncirus trifoliata, and they usually fail in their endeavours. Frost-hardy and bitter; tender and sweet - these seem to be the rules.
I am trying something rather different. With my interest in the Australian finger lime, and my love of the delicious pummelo, I thought I'd aim for a new cucumber-shaped and sized fruit. Will it be a Faustrummelo, or maybe a Faustrimedinelo?!
Why this combination? Well, apart from the amusing possibilities of crossing a large round fruit with a small, cylindrical one, there are some other reasons.
First of all, C. maxima produces seeds that are the result of sexual fertilisation. It does not produce exact clones of the parent, as some citrus varieties do.
Secondly, the leaf size and shape of the parent varieties mean that any seedling cross should be readily apparent without waiting years for fruit and then finding the cross failed. Only those obvious crosses with small leaves will need be grown on to maturity.
Thirdly the large size of the pummelo flowers should make pollenisation fairly easy.
Finally, I have a couple of suitable flowering potted plants. Although they are small, I think they could each carry a single fruit to maturity.
My first attempt was using pollen from a red-fleshed fingerlime plant, Microcitrus australis sanguinea, on to the stigma of a Red Pummelo flower.
The red pummelo plant about 75cms tall in July and August 2002.. The pictures were taken about 6 weeks apart. The somewhat lop-sided fruit has grown from golf-ball size to tennis-ball size. As you can see, the plant was attacked by a passing snail - but without damage to the fruit.
Unfortunately in mid September it was noticed that the base of the fruit had started to split, and mould was developing. In an attempt to repair this, the mould was carefully brushed off and the damaged area treated with the protective graft coating Lac Balsam. Will this allow fruit and seeds to keep growing??
Finally, by mid October the split had widened to a chasm and while inspecting the fruit one morning it fell off in my hand. It was now about 8cms diameter.
Inside some of the fruit segments were reasonably well developed -about 5cms long - but there was no trace of any seeds at all!
17th October 2002 So, the hybridisation attempt with this fruit has failed. Even if the fruit had not split and continued to grow, I don't think any seeds would have been produced. Either the pollen was sterile, the fertilisation process was imperfect or the parent combination incompatible. Is it worth trying again next year?
The second attempt was with pollen from a Faustrimedin - 1997 seedling - on to a Goliath pummelo.
Goliath Flower Close-up. Notice that I have removed all the original pollen bearing anthers to avoid self-pollination. The flower was prised open to do this, and some damage to the petals can be seen.
A day later, the faustrimedin flower was carried to the pummelo flower and its pollen transferred to the stigma. As this was sticky, I left the whole faustrimedin flower in place rather than try and remove it.
The Goliath pummelo, about 75cms tall. The pollinated flower is clearly visible in the left picture. When the fruit began to develop all other flowers were removed. The fruit, after about six weeks, is golf-ball sized; after 3 months, the size of a small orange.
In mid-January 2003, something was clearly amiss with this plant. The leaves started to wilt and drop. The fruit, which had just about turned yellow, was soft and flabby and clearly not growing. Perhaps I had over-watered in cool conditions and the roots were rotting? Anyway, I decided that the fruit needed to be removed in order not to stress the plant further. At this point it was 7.5cms diameter - medium orange sized. When I cut the fruit open I was pleased to see plenty of seeds. Though probably not fully mature and rather small for pummelo seeds, I think they stand a chance of germinating. So I have sown them in small pots and eagerly await developments!
The remaining seedlings are at last just starting to grow again. There are 8 with seed leaves, and another 2 with the shoot-only condition. There is however one very interesting observation. As far as I can recall, new growth of Pummelo's is always green; new growth of the Finger Lime and the hybrid Faustrimedin is dark purple. One seedling is definitely producing this dark-purple growth. So, unexpectedly, and without having to wait for leaf-shape comparison, I believe this must be a true hybrid.
By the way, the original Goliath plant has now died. I managed to take a couple of 'buds' from it, and these are still alive. But I certainly won't be able to repeat the experiment this year!
19th May 2003. Most of the seeds germinated, but that's where the problems started. They just refused to grow. Some produced a single shoot, about 1" (2.5cms) long and stopped. Others formed small 'seed-leaves' and stopped. In spite of having sterilized the compost in a microwave oven, the fungal disease "damping off" now took hold, and many of the seedlings turned brown at soil level, keeled over and died.
PROGRESS REPORTS CONTINUE ON A NEW PAGE: HYBRID SEEDLINGS
page updated 26Aug02, 10Sept02, 17Oct02 13Jan03, 19May03. re-built 22Feb17