Seedless Kishu: The Tiny Wonder

By Peter Chaires|November 18, 2011

The Mukakukishu (Mukaku) is commonly called the Seedless Kishu. Its fruit is very small, soft, easy to peel, has good flavor and color, and is absolutely seedless. It tends to mature mid-season. When considered on its own merits, the Seedless Kishu has limited commercial potential. It ranges in size from a golf ball to half of a golf ball. Although some creative and enterprising citrus farmers in California’s Ojai Valley successfully grow, pack, and market the fruit, it is widely considered a novelty or at best, suitable for roadside stands and dooryard purposes. The Seedless Kishu is too small to run on most conventional packinghouse equipment and too soft to survive in conventional packaging.

So why is the Seedless Kishu “all the buzz” in the citrus community, and why is it so important to Florida’s fresh specialty industry? The answer is simple: breeding.
The Seedless Kishu is a unique mutation that is female sterile, but male fertile. Therefore, its pollen can be used in breeding, with approximately 50% of the progeny expected to be seedless. Fruit from some of the Seedless Kishu hybrids may be too small for commercial applications, but it is hoped that others will incorporate its multiple positive characteristics while retaining the fruit size of the female parent.

Making It Work

The female sterility trait is under single gene control, and seedlessness is dominant. Therefore, the seedless trait segregates approximately 1:1 in hybrids of the Seedless Kishu with other mandarins. The Seedless Kishu has been used extensively in Japanese citrus breeding programs, with several advanced generation hybrids now produced and under evaluation. Going to second or third generation crosses is important to improve fruit quality characteristics (fruit size, shelflife, etc.), as well as tree vigor and health. The Seedless Kishu is being used in all Florida breeding programs, with some of the earliest crosses now fruiting, and second generation crosses in the works.
Although Seedless Kishu pollen appears visually to be of poor quality, it has proven to be especially fertile. The same is true of pollen from first generation hybrids at the UF/IFAS Citrus Research and Education Center in Lake Alfred. An additional bonus for the citrus breeders is that Seedless Kishu seems to confer shorter juvenility. So, times between successive generations will be minimal. Dr. Jose Chaparro recently developed molecular markers to select for seedlessness at the early seedling stage. These markers appear to be most useful when the crosses are of a specific pedigree. Their application to second or third generation crosses is being explored.

Addressing Accessability

Seedless Kishu budwood is available from DPI, and may be a niche market variety for roadside stands and those willing to harvest using clippers and explore innovative machinery and packaging. For everyone else, the Seedless Kishu provides our UF/IFAS and USDA-ARS breeders with a unique tool that has the potential to accelerate the development of marketable seedless mandarins. We will soon see progeny of Seedless Kishu crossed back with traditional Florida specialty varieties, as well as crosses using specialized parents known to confer marketable traits. Although this covers our introduction to this amazing little fruit, you will undoubtedly hear more soon.

Dr. Fred Gmitter, UF IFAS, co-authored the article. Dr. Greg McCollum, USDA-ARS, also contributed to this article.