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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' Sioux', 'Riverside', and 'Burkett' seedling rootstock. Tree and 'Curtis' seedling rootstock as compared to 'Apache', damage caused by a May freeze was directly related to bud growth and was influenced by scion and rootstock. Improved pecans are the result of vegetative propagation of selected cultivars on seedling rootstock. Seedling rootstock are grown from open-pollinated seed of many cultivars, with particular seed stocks being preferred in different regions (Gast and Overcash, 1980; Grauke, 1991; Thompson, 1990). For the production of seedling rootstock, nurseries choose seed stocks that have high levels of terminability , uniformity, and vigor (Grauke, 1991; Madden, 1978; Yarnell, 1934). Empirical ob- servations of seed stock differences have been confirmed by research. Differences in the percentage of nuts germinating, the earliness of germination, and the size of resulting seedlings have been reported between open-pollinated seed nuts from various cultivars (Grauke and Pratt, 1985). Little effort has been made to characterize differences arising between grafted pecan trees as a result of seedling rootstock, although rootstock is often cited as a potential source of varia- bility. Madden (1976) stated that seedling variability was "one of the primary reasons for lack of uniformity of nursery stock and orchards wherever pecans are grown. " When rootstock has been a controlled variable in tests, significant differences have been apparent. Sitton and Dodge (1938) reported that 'Schley' trees on 'Moore' seedling rootstock were 1.15 times larger and yielded 1.5 times more than 'Schley' trees on ' Waukeenah' seedling rootstock. Mielke (1981) reported differences in sur- vival, tree size, precocity, and yield as a function of rootstock. The occurrence of variability as a function of rootstock is important for two reasons: 1) sources of variation must be con- trolled in tests attempting to monitor cultivar performance and 2) selection criteria for rootstock improvement could be devel- oped by systematic evaluation of rootstock differences. This report documents differences in stages of bud growth in trees as influenced by rootstock and scion. The study was de- signed to address the following questions: 1) Can field-grown seedlings of the open-pollinated seed stocks commonly used in Open-pollinated nuts of 'Apache', 'Burkett', 'Curtis', 'El- liott', 'Moore', 'Riverside', and 'Sioux' were obtained from the U.S. Dept. of Agriculture, Brownwood, Texas, from a com- mercial nursery and from the Pecan Research-Extension Sta- tion, Louisiana State Univ., Shreveport, Each seed stock was obtained from only one source. All seed were stratified Jan. 1983 in moist sphagnum in plastic bags at 2 to 4C. In May 1983, nuts were planted in a nursery at the Pecan Station in a randomized complete-block design with seven seed stocks in each of 14 blocks. The site had a 2% downward slope from south to north and a 1% downward slope from west to east. Blocks were designed to account for slope in two directions. In each block, 32 nuts of each seed stock were planted 20 cm apart in rows 1 m apart with one seed stock per row. The diameter 5 cm above the ground was determined for each tree in the nursery in Jan. 1985. The 338 trees used in this test were selected for size uniformity from among the total. During Spring 1985, each seedling was either grafted with 'Candy', 'Cape Fear', or 'Stuart' scions or left ungrafted. Ungrafted trees were pruned comparably to the grafted trees at time of grafting. The number of trees of the various treatment combinations is shown in Table 1. The stage of bud growth was recorded for each tree 19-20 Mar. 1986, using the following scale: 1 = dormant buds; 2 = outer scale split; 3 = bud swell; 4 = inner scale split; 5 = leaf burst; 6 = leaf expansion (Wetzstein and Sparks, 1983). Data were subjected to analysis of variance using the General Linear Model (GLM) procedure of the Statistical Analysis Systems (SAS) program. Least-squares means were

Pecan Bud Growth and Freeze Damage are Influenced by Rootstock