Just harvested Marsh grapefruit trees on Murcott rootstock at age 3.5 years in a trial planted 15 by 22 feet on Pineda sand in 1990 near Fort Pierce, Florida. (Barney Greene cooperator)
By Bill Castle and Luiz A.B.C. Vasconcellos
Maybe it’s time to try a scion as a rootstock! Murcott is widely known as a scion variety, but it might be an interesting rootstock based on grower experience in Brazil as well as rootstock trial results and some commercial use in Florida.
Mandarin rootstocks and their hybrids have generally good horticultural traits, especially Cleopatra mandarin, which appears to be a rootstock less affected by HLB than others. Murcott is a presumed mandarin hybrid. Seeds of it are easily obtained, germinate readily and produce uniform populations. Unlike Murcott as a scion, Murcott seedlings as a rootstock seem to be budded easily with virtually any scion.
Murcott rootstock was included in four now concluded cooperator trials located in the central and east coast areas of Florida. The trees performed above average by conventional horticultural measures. To see the details about Marsh grapefruit, Hamlin, Navel sweet orange and Bearss lemon trees on Murcott rootstock and how they compared with those on other standard rootstocks, go to the Citrus Rootstock Selection Guide and search Murcott. A list of 14 publications is produced. See numbers 4, 7, 8 and 9.
Current images of unirrigated Pera sweet orange trees planted 12 by 20 feet in Brazil (Alpha Citrus) in 2003 on Murcott (left) or 2001 on Rangpur lime (right) rootstock. The incidence of blight so far among the trees on Murcott or Rangpur is negligible; the loss to HLB is 5 percent and 10 percent, respectively. Yield in recent seasons has been about 3 to 4 boxes per tree for both rootstocks.
In Brazil and Florida, trees on Murcott are moderately vigorous with good cropping, fruit size and juice quality. They do not exhibit the same delayed entry into bearing as experienced with some varieties on Cleopatra mandarin. Several of the Florida trials were conducted when blight was a major concern within the industry. In all cases, tree survival on Murcott was never less than 92 percent over the 7 to 12 years of the trials. It is for all of these reasons that Murcott and various mandarins have been used as parents in many rootstock breeding programs around the world, including those at the University of Florida Citrus Research and Education Center in Lake Alfred and at the U.S. Department of Agriculture’s Horticultural Research Lab in Fort Pierce.
Whether Murcott would provide any advantage regarding HLB when moved from the top of the tree, where it behaves poorly, to the bottom of the tree is an open question. Nevertheless, it is intriguing to consider possible outcomes in small-scale plantings with trees of any scion variety on Murcott planted along with many other new rootstocks needing additional commercial horticultural and HLB evaluation.
Bill Castle is professor emeritus at the Citrus Research and Education Center in Lake Alfred; Luiz A.B.C. Vasconcellos is a citrus consultant in Brazil.
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