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  • Author or Editor: L.J. Grauke x
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Abstract

At the meeting of the Crop Advisory Committee for Pecans and Hickories held on 24 Sept. 1984 in Albany, Ga., a question was raised concerning the legitimate scientific name of the pecan tree. Two names are currently in use: Carya illinoensis (Wang.) K. Koch (3, 6, 7, 10, 12, 19) and Carya illinoinensis (Wang.) K. Koch (1, 2, 11, 18, 21). Current usage is heavily in favor of the former epithet. When the 2 names were used as key words in the BIOSIS Previews computer search file for articles written between 1977 and the present, 199 were retrieved under C. illinoensis, whereas only 1 was found under C. illinoinensis. Since Hortus Third uses the latter epithet, articles on pecan submitted for publication in horticultural journals are occassionally returned to their authors for revision. The purpose of this paper is to trace the history of the nomenclature of the pecan as it relates to this dispute and in the process, demonstrate that the strict rules of scientific nomenclature and common sense can both be satisfied by the use of the epithet Carya illinoensis.

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The genus Carya is represented in North America by two Sections, with 14 species. Section Apocarya includes 4 U.S. and 1 Mexican species, all of which are diploid (n=16). The only commercially important Apocarya species is pecan, Carya illinoinensis (Wangenh.) K. Koch. Utilization and possible dissemination of pecan by man is evident in the archeological record to 6000 B.C. Patterns of genetic diversity in pecan in relation to geographic origin will be discussed for both native and cultivated trees. Other species of section Apocarya will be introduced and their potential role as rootstocks or for cultivar development through interspecific hybridization will be discussed. Section Carya includes 9 species, some of which are diploid (n=16) and some tetraploid (n=32). Horticultural selection has been greatest in the diploid species of the section [C. ovata (Mill.) K. Koch and C. laciniosa (F. Michx.) Nutt.]. Native species distributions and prominent cultivars will be discussed, along with problems associated with commercial culture of hickories.

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Seven open-pollinated pecan [Carya illinoinensis (Wangenh.) K. Koch] stocks were grown in a nursery in blocks. Bud growth of ungrafted seedlings was influenced by rootstock, with growth being more advanced on `Curtis', `Elliott', `Apache', and `Sioux' seedlings than on `Moore', `Riverside', and `Burkett'. Bud growth of grafted trees was influenced by scion, with growth of `Candy' being most advanced, while `Cape Fear' trees were more advanced than `Stuart'. Growth of `Candy' grafted trees was affected by rootstock, with growth being more advanced on `Elliott' and `Curtis' seedling rootstock as compared to `Apache', Sioux', `Riverside', and `Burkett' seedling rootstock. Tree damage caused by a May freeze was directly related to bud growth and was influenced by scion and rootstock.

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Putative resistance to the yellow aphid complex (Monellia caryella (Fitch) and Monelliopsis pecanis Bissell) in the `Pawnee' pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivar was first noted in greenhouse tests by rating cultivars for relative amounts of honeydew on adaxial leaf surfaces. This resistance was confirmed in two field tests monitored from mid-June to mid-Oct. `Pawnee' supported significantly lower aphid populations during every rating period when relatively large numbers of these insects were present. `Navaho' also showed resistance, with `Desirable' having intermediate resistance and `Stuart' being very susceptible. Insect populations were also monitored on the four quadrants of each tree, with this quadrant effect being significant in only one test. This test had the highest populations on the West and lowest populations on the East.

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The commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] nursery industry relies on open-pollinated seed for rootstock production. Current choice of seedstocks by commercial pecan nurserymen was surveyed by telephone. Nurseries were called if they appeared in the directory used for the 1994 release of `Navaho'. Factors influencing the choice of seedstock include seed availability, nut fill, nut size, nut shape, seedling vigor, stand uniformity, and root characteristics. Local availability is important in the choice of seedstock. Those who harvest from their own trees usually credit the seedstock with other valuable characteristics, such as improved germination or vigor. Those who purchase seed usually target a preferred seedstocks for particular reasons but plant available seed in its absence. Well-filled nuts are recognized as being important for good germination. Small nuts are often preferred, especially when seed is purchased because more nuts per pound increases potential production. Round nuts are generally preferred over long nuts due to improved performance in some mechanical planters. Distinct regional preferences are apparent in the choice of seedstocks. Regionally preferred seedstock selections are generally validated by a survey of the research literature. Patterns of selection are consistent with climatic and geographic constraints. Tree procurement patterns have changed: many small nurseries have gone out of business, many large nurseries transport trees far from the nursery for sales, and quarantine restrictions have altered procurement patterns in Arizona. Recommendations are made to nurserymen, pecan growers, and researchers concerning continued progress toward improving regionally adapted pecan rootstocks through seedstock selection.

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Thirty-six cultivars and 948 seedlings from 15 controlled crosses in the U.S. Dept. of Agriculture-Agricultural Research Service pecan [Carya illinoinensis (Wangenh.) K. Koch] breeding program at Brownwood, Texas, were rated for susceptibility to nut scab [Cladosporium caryigenum (Ell. et Lang.) Gottwald] to determine heritability of this trait. Differences between parents and progenies, and within progenies, were highly significant. Within most families, a complete range of resistance reactions were evident, from fully susceptible to fully resistant. Heritability of resistance was determined by regressing individual progeny values on female, male, and midparent values, with the midparent heritability estimate being the highest (0.54). This moderate level of additive gene action and the identification of superior parents in this study will contribute to the efficiency of breeding resistant cultivars.

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Thirteen cultivars of pecan [Carya illinoinensis (Wangenh.) K. Koch] were monitored for bud break, pollen shed and stigma receptivity for 4 years at LSU Pecan Station, Robson, LA. Cultivars were generally consistent in displaying clear patterns of protogyny or protandry, although patterns were uncertain for some cultivars in some years. Mean dates of cultivar phenology varied significantly by year. Years with warm winter and spring temperatures had earlier seasons of growth and flowering than years with cooler temperatures. The duration of pollen shed and stigma receptivity varied between years. Protogynous cultivars, as a group, had greater bloom overlap than protandrous cultivars, although overlap varied between years for both dichogamy classes. The sequence of cultivar flowering relative to other cultivars varied between years, resulting in variable amounts of bloom overlap between cultivars in different years.

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