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Author Topic: Pressure Is on to Pick and Plant Citrus Winners  (Read 289 times)

A.T. Hagan

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Pressure Is on to Pick and Plant Citrus Winners
« on: October 30, 2017, 02:28:58 PM »

Feedback from citrus variety surveys help determine which selections are worth vetting further.
Photo by Paul Rusnak

Of all the stones being thrown at HLB, the development of tolerant or resistant rootstocks and scions is among the rocks that could deliver a long-term solution to the disease. The disease itself has flipped the citrus breeding game as researchers widen the search for variety winners.

Peter Chaires, Executive Director of the New Varieties Development & Management Corp. (NVDMC), says a look at pre-HLB days compared to today provides historical context.

“On the processed side of the ledger, there had been very little interest in new oranges before HLB,” Chaires says. “Breeders were working on them to some degree, but most growers were perfectly happy with Hamlin, Mid-Sweet, Pineapple, and Valencia. Since HLB, the breeding programs have really put their foot on the gas to not only get the most promising processing-oriented scions released, but to continue to fill the pipeline with more material — all of which has superior traits. Field screenings for robust or enhanced performance in the face of HLB is a necessary part of this program.

“During this time, The two UF/IFAS OLL’s, plus ‘Valquarius’ and the ‘Vernia’ have been made available. More orange hybrids that show enhanced tolerance — and orange-like characteristics but that are not 100% sweet orange — are making their way into trial plantings. Breeding oranges is not like breeding mandarins. It’s a much slower process with fewer development options.

“On the fresh side, the number of developed and released selections has increased drastically. Whereas there used to be one release every 20 years or so, we have seen approximately 22 fresh selections made available through the accelerated programs and a number of private or proprietary selections come into Florida for trial.”

The Challenge

With so much material in the pipeline, it poses a challenge in the development and release process. There was a need to slow down development to learn more about the viability of what is already available.

“In recent years, fewer crosses were made and a greater emphasis has been placed on evaluation,” Chaires says. “Some evaluations are more formal designed experiments, including the collection of hard data, while others are observational.

“What we do know is that breeding cannot be turned on and off like a light switch. As new parents demonstrate promise and new techniques are developed, we must continue to feed the pipeline — though not at the pace we did a few years prior. Growers and nurseries need varieties with superior traits and with the ability to withstand HLB, preferably with minimal care.”

Jude Grosser, a Professor of plant cell genetics for UF/IFAS, who is seeking the best rootstock/scion combinations, says it is complicated because many of the rootstocks in established trials were developed to solve other problems before HLB came along.

“We need to balance this with looking for the ‘home run’ rootstock — which should come from new selections being screened right off the bat for ability to provide protection against HLB in a grafted scion,” Grosser says. “I believe we are looking for a needle(s) in a haystack. So, the bigger the haystack, the better the odds of finding something that will work.”

Grosser has tested thousands of rootstocks hybrids using his “gauntlet” approach. After screening for initial soil adaptation and Phytopthora viability, the more robust candidates are grafted with HLB-infected Valencia and grown off. This is a quick way to see if the rootstock can mitigate the disease.

“I have been doing this for six years, and I have a few hybrid rootstocks that look especially promising,” Grosser says. “Two of which we are producing seed adequate for large scale testing.”

Grosser adds another complicating factor is understanding how these new selections will react to various nutrition programs. Because not all trials have the same program, it can make it harder to make comparisons among trials at different locations.

It's a long article with a lot of links so go there for the rest of it.


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