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- Author or Editor: Robert Marquard x
Abstract
Nut weight and percent kernel are most commonly used to estimate size and kernel development of pecans (Carya illinoensis). However, because of differences in shell thickness, nut specific gravity (NSG) is considered, by some, to be more appropriate than percent kernel as a measure of kernel development (2, 3). Another disadvantage of measuring percent kernel is that it is a time-consuming procedure that requires care in nut cracking and kernel extraction.
More than 30 pecan [Carya illinoensis (Wangenh.) K. Koch] seedlings of `Riverside' have exhibited an unusual leaf morphology described as lace-leafed. Seedlings have relatively low vigor, compound leaves, and leaflets with deeply serrated margins with higher length: width ratios than normal seedings. Some leaves are both pinnate and palmately compound and some leaflets are lobed. The segregation ratio of lace-leafed seedlings for one gene controlling a polymorphic genetic marker supports the hypothesis that lace-leafed seedlings result from selfing of `Riverside.' Nine percent (three of 33) of seedlings derived from selfing of `Riverside' exhibited the lace-leafed morphology, suggesting a recessive trait controlled by one or two genes. The gene(s) controlling this phenotype in pecan is arbitrarily designated the ll gene(s).
Abstract
Isozyme banding patterns, elucidated by starch gel electrophoresis, frequently are simply inherited and also useful tools in horticultural research (4). An earlier paper (1) documented that malate dehydrogenase (MDH; EC 1.1.1.37) in pecan is a dimer controlled by at least one polymorphic gene with two alleles (Mdh-1). Two of 66 pecan cultivars were characterized for Mdh-1 and produced an additional Mdh-1 band that remained unexplained (1). Results from controlled crosses confirm that two additional alleles exist for the Mdh-1 locus, but are rare among cultivars and occur at a frequency of about =1%. Controlled pollinations produced seedlings with MDH phenotypes not previously observed in pecan.
Abstract
Leaf to fruit ratios of 2, 4, 8, and 12 were created on girdled shoots of three cultivars of pecan (Carya illinoensis (Wangenh.) C. Koch). Girdling of fruiting and vegetative shoots reduced net photosynthesis to nearly 30% and 3%, respectively, of the ungirdled “checks.” Differences in photosynthetic rates among the various leaf to nut ratios were not detectable. Two leaves, equivalent to 575 cm2 of leaf area, were sufficient to fill one pecan kernel of ‘Sioux’ or ‘Western’. A ‘Mohawk’ leaf to fruit ratio of 4 produced nuts superior in quality to those supported by two leaves. Girdling tended to increase shoot carbohydrates, and starch accumulation was related to leaf to fruit ratio in ‘Mohawk’.
Abstract
The growth inhibitors paclobutrazol and flurprimidol were applied to the roots of greenhouse-grown pecan seedlings [Carya illinoensis (Wangenh.) K. Koch] at 0, 0.02, 0.10, and 0.50 mg a.i. Treatment with paclobutrazol reduced tree height, stem weight, and increased the root:shoot weight ratio. Flurprimidol reduced tree height, leaf area, internode length, and stem weight. Promalin (50 ppm GA4+7 plus 6-benzylamino purine) applied as a foliar spray enhanced lateral branching, increased stem diameter and total dry weight, and reduced the root:shoot weight ratio. Paclobutrazol appeared to be more affective than flurprimidol in reducing shoot growth. Neither growth inhibitor significantly affected the rate of net photosynthesis.
Six phosphoglucomutase phenotypes were observed in pecan [Carya illinoensis (Wangenh.) K. Koch] progeny after controlled pollinations. At least one locus (Pgm-1) is present that controls polymorphism of phosphoglucomutase (PGM) isozymes in pecan. The inheritance appears simple with three observed alleles. However, progeny produced from two crosses resulted in significant deviation from the expected segregation ratios. Out of 65 named cultivars, 61 were of a single phenotype, and two of six possible phenotypes were not observed. Only one region of PGM activity was consistently expressed by gel electrophoresis from pecan tissue.
Abstract
Nuts produced from controlled crosses of ‘Western’ pecan [Carya illinoensis (Wangenh.) C. Koch] pollinated with ‘Wichita’ were 20% heavier and 12% larger by volume than self-pollinated nuts. The inherited biochemical marker of malate dehydrogenase was used to quantify outcrossing in a ‘Western’ orchard with ‘Wichita’ as the pollinator. The frequency of cross-pollination declined with distance from the pollinator, and the linear equation y = 53.9 − 6.1x was derived to estimate percent cross-pollination (y) in row (x) away from the pollinator. A model to estimate relative orchard production predicts maximum efficiency of a ‘Western’ orchard when the frequency of the pollinator is 25% to 33%. Nut quality of ‘Western’ field samples was positively related to percent cross-pollination of the sample. Cross-pollination under field conditions of ‘Western’ by ‘Wichita’ increased nut weight and volume 31% and 16%, respectively.
Abstract
Isozyme banding patterns of malate dehydrogenase (MDH) and phosphoglucose isomerase (PGI) were polymorphic in leaf and pollen extracts of pecan [Carya illinoensis (Wangenh.) C. Koch], Both enzyme systems produced two prominent anodal zones of activity with similar banding patterns expressed from leaves and pollen. The fast-migrating MDH region (Mdh-1) was polymorphic, with three banding patterns. Segregation ratios support a model that Mdh-1 is a dimer controlled by a dimorphic locus. The slow-migrating MDH region was monomorphic and produced five densely staining bands. The fast-migrating PGI zone also was fixed in all samples assayed. Six banding patterns were detectable in the less-anodal region (Pgi-2) and produced one of three single-handed or three triple-banded patterns in leaf extracts. Segregation ratios indicate Pgi-2 is controlled by three alleles at a single locus. Mdh-1 and Pgi-2 genotypes are included for 66 cultivars and based on Mdh-1 inheritance; ‘Kiowa’ has been incorrectly reported to be parented by a ‘Mahan’ × ‘Odom’ cross. Genes controlling Mdh-1 and Pgi-2 were not closely linked. Enzymes remained active and stable in pollen stored for 30 months at −20°C and in leaves stored at 4° for 45 days. Frozen enzyme extracts remained stable for 18-24 days and dimethyl sulfoxide [Me2SO (DMSO)] prolonged extract storability.
In vivo pollen tube growth of pecan [Carya illinoinensis (Wangenh.) K. Koch] was estimated to be ≈ 150 μm·hour-1 from 3 to 8 hours postpollination. Pollen tubes averaged 47, 194, 405, and 946 μm after 2, 3, 4, and 8 hours postpollination, respectively. Pollen tube growth was strongly influenced by temperature, and in vitro studies demonstrated pollen germination and tube growth were optimal at 27C for `Cape Fear' pecan. In in vivo studies, tubes of cross-pollen did not grow significantly faster than tubes of self-pollen. Pollen tubes of water hickory [C. aquatica (Michx. f.) Nutt.] grew significantly faster than those of C. illinoinensis. Bitternut [C. cordiformis (Wangenh.) K. Koch] and mockernut hickory (C. tomentosa Nutt.) pollen tubes grew significantly slower on pecan stigmas than did pecan pollen. Pollen arriving first on the stigma has a decided advantage for fertilization success of pecan. The fertilization success rate of pecan pollen arriving 24 hours after first pollen arrival was <3%.