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Pecan scab, caused by the plant pathogenic fungus Fusicladium effusum, is the most destructive disease of pecan. Little is known of the population genetic diversity of this pathogen. In this study, microsatellites were mined from the F. effusum genome, and flanking primers were subsequently designed. A total of 275 microsatellites were screened, and 33 selected primers produced reliable, polymorphic markers against 46 isolates of F. effusum from 11 diverse locations in the southeastern USA. The number of alleles per microsatellite locus ranged from two to 17, and the polymorphic information content ( PIC) from 0.475 to 0.911. A unique pattern informative combination ( UPIC) analysis of three groups of 12 isolates each and 33 primers consistently showed a minimum number of markers required for the maximum discrimination of isolates equal to 3. The characteristics of the unique patterns ( UP) and informative contents ( IC) were very similar. However, the primers that were selected by UPIC were not necessarily the same for each of the three groups. Using all 46 isolates showed each locus was polymorphic, with a single-population level Shannon's information index of 1.516, indicating substantial diversity. These markers show a range in polymorphic content and power of discrimination that will be valuable tools for studies of genetic diversity in F. effusum. [ABSTRACT FROM AUTHOR]

Fusicladium effusum infects pecan causing yield loss, but no information is available on the genetic diversity of F. effusum. Randomly amplified polymorphic DNAs ( RAPDs) and universally primed polymerase chain reaction ( UP- PCR) were compared to detect polymorphisms on a group of 20 isolates of F. effusum from 11 geographical locations in the southeastern USA. Two tests (run 1 and 2) of both the RAPD and UP- PCRs were conducted to assess the repeatability of the methods, and the markers scored on agarose gels. In addition, the UP- PCR markers from run 1 were scored using an automated capillary system. Both RAPDs and UP- PCR markers detected a high level of polymorphism among the scored markers (92 and 91% of RAPD markers, and 86 and 87% of manually scored UP- PCR markers in run 1 and 2 were polymorphic, respectively; 93% of UP- PCR markers were polymorphic when scored using the automated system). Unweighted paired group method of arithmetic averages ( UPGMA) analysis showed both RAPDs and UP- PCR markers individually identified each isolate, producing three groupings, but only the groupings based on run 1 and 2 of the UP- PCR contained the same isolates. Bootstrap analysis based on the Dice coefficient produced phenograms from the UP- PCR data with weak to moderate node support (≥54) for the primary branch, but no support for the RAPDs data (≤34). A Mantel test of runs 1 and 2 using RAPDs or UP- PCR showed good agreement ( r = 0.8761 and 0.8289, p < 0.0001), but poor agreement between RAPDs and UP- PCR. UP- PCR results based on the interisolate Dice coefficients showed a weak to strong association with distance. Based on these results, both RAPDs and UP- PCR markers were capable of demonstrating polymorphisms and identifying relationships among isolates of F. effusum; however, UP- PCR markers appear to be more reliable. [ABSTRACT FROM AUTHOR]

Semi-parasitic evergreen mistletoe (Phoradendron flavescens Nutt.) is an increasingly serious weed causing loss of nut yield and tree vigor in pecan [Carya illinoinensis (Wangenh.) K. Kochl orchards of the southeastern United States. Several herbicides and growth regulators were evaluated for efficacy against mistletoe. The dimethylamine salt of 2,4-D proved to be an effective control agent. Ethephon, glyphosate, paraquat dichloride, and polyborate exhibited little or no long-term efficacy. The dimethylamine salt of dicamba also killed mistletoe, but exhibited potential for harming host trees. Dormant season treatment of mistletoe clusters with 2,4-D reduced photosynthesis by about one-third soon after treatment, and by ≈90% from 6 to 16 weeks posttreatment, but clusters did not die until ≈4 months posttreatment. Host limbs, less than ≈3 cm in diameter at the site of mistletoe attachment, usually died within 12 months of 2,4-D treatment of the associated mistletoe cluster. Treatment of entire host trees with 2,4-D did not harm trees if applied prior to ≈1 week of budbreak. Spot treatment of mistletoe clusters, with 2,4-D at 1.2 to 2.4 g⋅L-1 a.i. (plus 2% crop oil), ≈2 to 3 weeks before budbreak, gave effective long-term control of mistletoe. The inclusion of a crop-oil in the 2,4-D spray greatly increased efficacy. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon). [ABSTRACT FROM AUTHOR]

Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees exhibit nickel (Ni) deficiency in certain orchard situations. The symptoms are manifest as either mouse-ear or replant disorder and in certain situations are associated with nematode parasitism. A field microplot study of pecan seedlings treated with either Meloidogyne partityla or Criconemoides xenoplax or both found that parasitism by M. partityla can result in enhancement in the severity of mouse-ear symptoms and a reduction in foliar Ni concentration. The Ni threshold for triggering morphological symptoms in young developing foliage was between 0.265 and 0.862 µg·g-1 dry weight, while the threshold for rosetting was between 0.007 and 0.064 µg·g-1 dw. Results indicate that parasitism by M. partityla is a contributing factor to the induction of Ni deficiency in pecan and raises the possibility that nematode parasitism and Ni nutrition can be contributing factors to many plant maladies. [ABSTRACT FROM AUTHOR]