cS~-~ r -,J~r a ;S~C:+~6 Bz ' ~; i-~q ~1 -1, ,";P~;. ... BULLETIN 484 DECEMBER 1976 PERFORMANCE of SELECTED APPLE ROOTSTOCK in the PIEDMONT AREA of CENTRAL ALABAMA, 1965 - 1975 AGRICULTURAL EXPERIMENT R. Dennis Rouse, Director STATION AUBURN UNIVERSITY Auburn, Alabama CONTENTS Page INTRODUCTION -- - - - - - - - -- - - - - - - - -- - - - - - - -DESCRIPTION OF EXPERIMENT ----------------------------- 4 6 6 RESULTS AND DISCUSSION--------------Tree Size and Leaf Area--------------------------------------------- Yield---------------------------------------------------------------- 9 Fruit Maturity ----------------------------------------- 10 Tree Mortality--------------------------------------------12 Woolly Apple Aphid Infestation-----------------------13 CONCLUSIONS---------------------------------------- 14 FIRST PRINTING 4M, DECEMBER 1976 Auburn University is an equal opportunity employer. Performance of Selected Apple Rootstock in the Piedmont Area of Central Alabama 1965-1975 W. ALFRED DOZIER, JR., HOYT E. BURGESS, W. A. GRIFFEY, E. L. MAYTON, A. J. LATHAM, H. J. AMLING, and C. A. KOUSKOLEKAS* INTRODUCTION A ROOTSTOCK for trees is one of the most important decisions made before establishing an apple orchard. In fact, the root system is just as important in the production of quality trees and fruit as is the scion variety which it supports. Thus, a wrong choice will penalize the grower for as long as the orchard is maintained. Some of the important characteristics that should be considered when selecting a rootstock are: (1) type of rooting system that it develops, anchorage, and performance in a given soil type and moisture condition; (2) effect on ultimate tree size and form; (3) ability of the rootstock to induce the scion variety to begin fruiting at an early age and bear larger yields each successive year; (4) influence on fruit size, color, and quality; (5) degree of resistance to certain insects and diseases; (6) adaptability and hardiness of the rootstock to climatic conditions and its effect on the hardiness of the scion variety; and (7) compatibility with the scion variety. Apple production has shifted from large, standard size trees on seedling rootstocks to smaller trees on size controlling (dwarfing) rootstocks. Newer plantings may be on semi-dwarf rootstocks and be free standing or be on the dwarfing rootstocks that * Respectively, Assistant Professor, Department of Horticulture; Assistant Superintendent, Piedmont Substation; Superintendent, Piedmont Substation; Retired Superintendent, Piedmont Substation; Associate Professor, Department of Botany and Microbiology; Professor, Department of Horticulture; and Associate Professor, Department of Zoology-Entomology. SELECTING 4 ALABAMA AGRICULTURAL EXPERIMENT STATION require support by trellising or staking. Mature trees that do not exceed 8 to 10 feet in height provide for efficient use of labor, by allowing harvesting and pruning to be done from the ground, and make spraying efficient. Size controlling rootstocks induce earlier fruiting and higher per acre yields, which lower per unit production costs, and improve overall fruit quality. The size controlling Malling Merton (MM) rootstock series are crosses of 'Northern Spy' with certain 'East Malling' (EM) clones. Desired characteristics of both parents are incorporated into the MM series: size control, resistance to woolly apple aphids, improved anchorage, scion compatibility, and precocity. DESCRIPTION OF EXPERIMENT An experimental planting was established in 1965 and 1966 on Hiwassee series soil at the Piedmont Substation, Camp Hill, to compare performance of the more promising rootstocks of the Malling Merton (MM) series with seedling rootstocks. Purpose of this evaluation planting was to determine the apple rootstock best suited for the Piedmont Area of Alabama. To achieve this end, rootstocks were evaluated for their influence on tree size, yield, fruit size, and maturity, and susceptibility of the rootstocks to root diseases and woolly apple aphid infestations. Rootstocks included in the study were MM 104, MM 106, MM 111, and seedling. Each rootstock was replicated 10 times with five trees per replication in a randomized complete block design. 'Miller Sturdeespur Delicious' was replicated eight times and 'Sundale Sturdeespur Delicious' was replicated two times for pollination. The Sundale Sturdeespur Delicious was top worked to 'Mollies Delicious' in 1968 and 1969. The planting was bordered on one side by a pollinator row of Mollies Delicious. Pollen was also furnished each season (1969-75) during bloom with beehive inserts. Trees on MM 104 and seedling rootstocks were planted in the spring of 1965 and the trees on MM 106 and MM 111 were planted in spring 1966. One-year-old apple whips of 1/2- to 5/8inch caliper were used. Trees were spaced 12 feet apart in rows, and the rows were 16 feet apart. This spacing is the equivalent of 227 trees per acre. The trees were trained to a modified central leader system. In the winter of 1972, and each pruning season thereafter, trees were reduced to a height of 9.5 to 10.0 feet with a Fossum tree pruner. Detailed hand pruning was carried PERFORMANCE OF SELECTED APPLE ROOTSTOCK 5 out after mechanical pruning. Vegetation on the orchard floor was controlled by using recommended herbicides in the row and mowing between rows. Soil pH and fertility levels were maintained according to soil test and foliar analysis recommendations. The Auburn University apple spray schedule was followed for insect and disease control. Trunk diameter, tree height, and tree width measurements were obtained in the fall of 1969, 1971, 1972, and 1975 and on July 14, 1976. Trunk diameter measurements were made 1 foot above the soil line. Measurements were made to obtain maximum tree height and tree width. Rootstock influence on leaf area was obtained by measuring 15 average size leaves from the fruiting spurs and the center of the terminal growth of one Red Delicious tree from each of the three replications. The area of each leaf was determined by length X width measurements. Yield data were recorded in pounds per tree for Red Delicious trees from 1969 through 1975, except in 1973. Effect of rootstock on maturity and red color development was investigated in 1971 and 1975. Twenty fruits from each of the eight replications were harvested each sample date. In 1971 the fruits were sampled August 6, 13, 20, and 27 and September 3 and 9. In 1975, the fruits were sampled August 5, 8, 11, 15, 18, 22, 25, and 29. Maturity indices investigated were fruit firmness, percent soluble solids, fruit size, ground color, flesh color, percent seed color, and percent red color development. From 1967 through 1973, dying and dead experimental trees were evaluated for root rot causal agents. Infected tree roots and stumps were evaluated in the laboratory for Xylaria mali Fromme black root rot infection. Isolates of X. mali were evaluated for pathogenicity to apple seedlings in the greenhouse. Identification of Armillaria or oak root rot Armillaria mellea (Vahl) Quel., white root rot Corticium galactinum (Fr.) Burt, and crown gall Agrobacterium tumefaciens (E. F. Sm. and Towns.) Conn was made according to symptoms and cultural characteristics of the pathogen. During July 1971, roots of all living experimental trees were sampled at five locations from the drip line to the trunk at a 6-inch depth and 12-inch width to determine woolly apple aphid infestations. Rootstock susceptibility to woolly apple aphid was evaluated on a 1 to 5 scale: 1 = no infestation or galling; 2 -= 6 ALABAMA AGRICULTURAL EXPERIMENT STATION light infestation or galling (on feeder roots); 3 medium infestation and galling; 4 = heavy infestation and galling (on roots of a portion of the tree); 5 = heavy infestation and galling on all roots. RESULTS AND DISCUSSION Tree Size and Leaf Area Trunk diameter of trees on MM 111 rootstock was smaller than on MM 104, MM 106, and seedling rootstocks throughout the experiment, Table 1. Trees on seedling rootstock measured larger in trunk diameter than trees on the other rootstocks, with the exception of trees on MM 104 in 1969, 1971, and 1976. Trunk diameter of trees on MM 106 was greater than on MM 111 rootTABLE 1. INFLUENCE OF ROOTSTOCK ON TREE SIZE OF MILLER STURDEESPUR DELICIOUS APPLE TREES, PIEDMONT SUBSTATION, 1969, 1971, 1 1972, 1975, AND 1976 Rootstockdiameter Trunk height Ft. Tree width Ft. 4.98a Tree in. 1969 MM 104------------------------------------------2.11a2 MM 106----------------------------------1.82b MM 111---------------------------1.56c Seedling---------------------------2.3ab 1971 MM 104--------------------3.02ab MM 106--------------------------------------- 2.74b MM 111--------------------------------------- 2.25c Seedling---------------------------------------- 3.15a 1972 MM 104-------------------------3.43b MM 106--------------------------------------- 3.28b 8.55a 8.60a 7.87ab 5.15a 4.41b 7.34b 10.69ab 5.07a 8.13a 11.46a 9.94b 11.54a 9.95bc 10.9Oab 11.46a 8.70a 7.72b 8.53a 7.O0ab 7.65a 6.22b MM 111------------------------------------Seedling---------------------------------------- 2.65c 3.93a 4.10b 3.81b 3.08c 4.58a 4.72ab 4.60b 3.72c 5.14a 9.41c 7.76a 8.43b 9.OOa 7.38c 1975 M M 104-----------------------------------MM 106-------------------------------MM 111--------------------------------------Seedling---------------------------------------1976 (July 14) MM 104-------------------------------------MM 106--------------------------------_---_-MM 111-------------------------------- ---- 9.29a Seedling ------------------------ _ -- trees on MM 106 and MM 111 were planted the following spring. 2 Values in a column followed hy the same letter are not significantly different (Duncan's Multiple Range Test, 5 percent level). 'Trees 11.22b 12.40a 10.20c 12.63a 11.17a 11.10a 8.83b 11.66a on MM 104 and seedling rootstocks were planted in spring 1965 and PERFORMANCE OF SELECTED APPLE ROOTSTOCK 7 stock and smaller than trees on seedling rootstock. Trunk diameter of trees on MM 106 rootstock was smaller than trees on MM 104, but the difference was significant only in 1969. Trees were hand pruned to a modified central leader system from planting through 1971 and allowed to attain their natural height and width. In the fall of 1971, trees on MM 111 rootstock were the smallest in height and width, except they did not differ in height from trees on MM 104 rootstock. The orchard was mechanically pruned to a height of 91/2 to 10 feet in late winter of 1972 and each season thereafter. In the fall of 1972, after mechanical pruning in the spring, trees on seedling and MM 106 rootstocks were the tallest and trees on MM 111 were the shortest. Trees on MM 104 did not differ in height from trees on MM 106 or MM 111 rootstocks. On July 14, 1976, trees on seedling and MM 106 rootstocks were the tallest and those on MM 111 the shortest. Width of trees was less on MM 111 rootstock than on the other rootstocks throughout the 11 years of orchard life. The one exception was in 1972 when there was no difference in width between trees on MM 111 and MM 104 rootstock. In the fall of 1975, the width of trees on seedling and MM 106 rootstocks was greater than the width of trees on MM 104 rootstock. When measured in July of 1976 with a crop of fruit, however, width of the trees on MM 104, MM 106, and seedling rootstocks did not differ. Throughout the 11 years of orchard life there has been a great, observable difference in tree vigor. Trees on MM 111 rootstock have not been as vigorous as trees on the other rootstocks and do not appear adapted to Piedmont growing conditions. Few lateral branches developed from the major scaffold branches and little terminal growth has been made. When pruning with a mechanical pruner, about 3 to 6 feet of excessive vegetative growth has been removed each season from the top of trees on MM 104, MM 106, and seedling rootstocks; however, no terminal growth has been removed from the top of trees on the MM 111 rootstock. In addition to observable differences in shoot growth, leaves of trees appeared sparse and smaller on MM 111 rootstock than on the other rootstocks in each growing season. In 1975, leaves on the fruiting spurs and terminal growth of trees on MM 111 rootstock were found to be smaller than leaves on trees on MM 104, MM 106, and seedling rootstocks, Table 2. Leaves r -. ,4A t 4I 9.i "> 26 st. ,44;i. ~~tda-l I"' i,A,) 1~ N,~ ?r;, :I '44ca '54.~ A' , 4 '-1 '4 4 - '~ ' 4 :2%i Typical appearance of trees on the four rootstocks tested are illustrated. Left to right are MM 104, MM 106, MM 111, and seedling. on the terminal growth of trees were larger in the case of trees on MM 106 rootstock than for trees on MM 104 rootstock. The leaves from the terminal growth of trees on seedling rootstock did not differ in size from those of trees on MM 104 and MM 106 rootstocks. Typical trees on the MM 111, MM 104, MM 106, and seedling rootstocks are shown in the color photographs on pages 8 and 9. The small, sparse foliage and lack of vegetative growth of trees on MM 111 rootstock contrast with the vigor of trees on MM 104, MM 106, and seedling rootstocks. Trees on seedling rootstock vere excessively vigorous. TABLE 2. INFLUENCE OF ROOTSTOcK ON LEAF AREA OF FRUITING SPURS AND TERMINAL GRow"IT! OF MILLER STURDEESPUR DELICIOUS APPLE TREES, PIEoDoNT SUBSTATION, 1975 Leaf area Rootstock Fruiting spurs Sq. cm 26 3 2 MM 104 S106--- -25.71' -17.56b M 111 Seedling . 4a 8. 2 1a Terminal growth Sq. cm 50.07b 54 . 1 6a 37.19c 50.58ab Values in a column followed by tie same letter are not significantly different (Duncan's Multiple Range Test, 5 percent level). 1f Yield Fruit set prior to 1969 was light and scattered. Inadequate pollination probably contributed to poor fruit set since the Golden Delicious' pollinators did not bloom with the Red Delicious v arietv. In 1968 and 1969, the pollinators we re top worked to 'Mollies Delicious, wxhich has bloomed with the Red Delicious variety each year. Golden Delicious pollen was furnished by use of beehiv e inserts each y ear starting in the spring of 1969. Collection of xield data wxas begn in 1969, Table 3. Trees on MI 106 hav e consistently produced the highest yields and trees on seedling and MIM 111 rootstock the lowest yields. Production of trees on MLM 104 and NITM 106 rootstocks has not v aried TABLE 3. INF-LUENCE OF ROO'ISTOCK' ON YIELD OF MILLED STURDEESPUR DELICIOUS APPLE TRiES, PIEDMONT SUBSTATION Rootstock 1969 Lb. 2 1970 Lb. 37.42a 30.20a 18.071) 19.20b Yield of fruit per tree 1971 Lb. lill1ab 13.0)5a 5.13b 4.88b 1972 Lb. 75.04a 7 44 8. a 44.71b 64.66a 1973 Lb. __ __ 1974 Lb. 38.86a 40.01a 29.70a 34.01a 1975 Lb. 58.31b 116.49a 61.00b 75.51b \IM 104 ____ .11.78a MIM 106 ___11.06a -6.99b \I\I 111 _ 3.34e Seedling Trees on MM 104 and seedling rootstocks were planted in spring 1965 and trees on MM 106 and NM 111 were planted the following spring. zvalues in a column followsed by the same letter are not significantly different (Duncan's Multiple Range Test, 5 percent level). 10 ALABAMA AGRICULTURAL EXPERIMENT STATION 10 ALABAMA GRICULTUA XEIMN TTO greatly, except in 1975 when trees on MM 106 produced twice as much fruit as trees on MM 104. Even though the per tree yield of trees on MM 104 and MM 106 did not vary greatly, the per acre yield on MM 106 would be much greater due to the higher loss of trees on MM 104 rootstock. Yield data were not collected in 1973 because the orchard was used for a growth regulator study; however, all trees set a good crop. Rootstock did not influence bloom date of the scion variety. All Red Delicious trees bloomed together each season. Fruit Maturity The influence of rootstock on maturity and red color development of Miller Sturdeespur Delicious apples was investigated in 1971 and 1975. Fruit reached a minimum level of' maturity for TABLE 4. EFFECT OF ROOTSTOCK ON MATURITY OF MILLER STURDEESPUR DELICIOUS APPLES, PIEDMONT SUBSTATION, 1971 Sample date Fimes ns Soluble solids Pct. 9.0 10.0 10.6 11.8 12.6 13.8 8.6 9.6 10.6 11.0 13.4 14.6 9.0 10.2 11.0 11.8 12.4 13.8 8.0 9.6 10.6 11.2 11.2 13.8 Red color Pct. 34.5 70.5 80.0 94.5 96.1 94.0 36.8 67.0 85.0 94.0 97.5 93.5 36.8 70.5 88.5 90.3 95.6 88.0 Ground color Fruit size In. 2.64 2.71 2.85 2.76 2.96 2.76 2.64 2.78 2.80 3.00 3.04 2.94 2.54 2.66 2.69 2.83 2.84 2.69 2.69 2.66 2.82 2.81 Flesh color C W/YT W/YT W /YT Y Y C w W/YT W/YT Seed color Pct. 17.3 80.0 84.5 89.0 100.0 97.0 12.5 68.0 88.5 96.5 99.0 99.0 22.3 50.5 84.0 97.0 99.0 97.0 31.5 65.0 84.0 99.5 MM 104 rootstock 23.1 8-6-71----------8-13-71-------- 23.0 8-20-71-------- 20.4 8-27-71-------- 22.4 G1 9-8-71 --------- 9-3-71-- ------- 20.8 16.9 G/YT G/YT G/YT Y Y C C/YT C/YT G/YT Y Y C C/YT G/YT G/YT Y Y MM 106 rootstock 22.7 8-6-71 -21.1 8-13-71-21.8 8-20-71 20.7 8-27-71 19.3 9-3-71 ---15.1 9-8-71 MM 111 rootstock 8-6-71---------23.5 8-13-71 --------- 23.1 8-20-71 -------8-27-71-------23.3 22.8 Y Y C W/YT W /YT W /YT W/YT C W /CT W/YT W/YT W/YT 9-3-71---------22.6 9-8-71----------- 17.6 Seedling rootstock 18.7 8-6-71 - -----21.2 8-13-71------8-20-71 --------- 20.3 8-27-71 -------- 23.7 22.6 9-3-71--------9-8-71- of 20 fruit. SG = -------- 16.9 = green; W white; Y = G 66.0 C/YT 67.5 C/YT 89.0 92.5 Y Y 84.5 Y 91.0 yellow; T = tint. 2.81 2.84 W/YT 100.0 98.0 Each value is the average PERFORMANCE OF SELECTED APPLE ROOTSTOCK 11 PERFORMANCE OF SELECTED APPLE ROOTSTOCK1 harvest by August 20 in 1971 and August 15 in 1975, tables 4 and 5. Rootstock did not have an appreciable influence on fruit maturity, size, or red color development. However, fruit from trees on MM 111 rootstock tended to be a little smaller and firmer and have slightly higher percent soluble solids than fruit from trees on the other rootstocks. The higher fruit firmness was due to the smaller fruit size. Fruit from trees on the MM 111 rootstock had more of the ment, but the color was not as deep a red as fruit from trees on TABLE 5. INFLUENCE OF ROOTSTOCK ON MATU~RIY OF MILLER STURDY DELICIOUS APPLES, PIEDMONT SUBSTATION, 1975 surface area with red color Ground color develop- Sample Soluble Firmdate solids ness Pct. MM 104 rootstock 10.3 8-5-751___ 18.2 9.0 8-8-75.__- 17.4 9.1 8-11-75___ 17.8 8-15-75-8-18-75-8-22-75___ 8-25-75.. 17.9 17.7 17.1 17.1 10.5 10.9 11.6 11.6 Red color Blush Total Pct. Pct. 34.5 41.7 36.3 50.2 48.1 60.5 48.0 44.0 31.1 Fruit size Flesh color Seed color In. 2.72 2.77 2.73 2.78 2.88 2.90 2.82 2.90 2.80 2.91 2.90 2.91 2.90 2.98 2.97 3.19 2.64 2.69 2.63 2.76 2.80 2.73 2.72 2.80 2.78 2.76 2.88 2.80 2.88 2.93 2.92 2.79 = tint. Pct. GYT GYT GYT GYT GYT YGT YGT YGT 1 12.1 8-29-75___ 15.6 MM 106 rootstock 10.0 17.5 8-5-75 9.2 8-8-75_____ 17.6 9.0 8-11-75___ 17.2 8-15-75_-. 17.9 10.3 80.6 81.8 83.0 87.5 86.7 91.2 91.3 84.2 73.7 82.9 81.3 89.6 89.2 89.6 89.6 84.5 78.4 81.1 85.2 87.0 91.4 90.4 90.0 91.4 68.3 70.3 81.3 86.7 85.9 88.0 83.7 80.3 rr~r\ = WGT WGT WGT WGT WYT WYT WYT Y WGT WGT WGT WGT WYT WYT Y Y WGT WGT WGT WGT WYT WYT WYT Y WGT WGT WGT WGT WYT WYT WYT Y 69.4 53.7 50.3 87.3 98.6 96.3 99.4 100.0 68.3 44.9 55.7 95.9 93.8 89.7 98.0 100.0 56.9 50.4 43.0 95.4 97.1 92.4 98.3 100.0 66.9 50.9 54.4 92.0 99.4 91.8 95.7 100.0 ----17.2 17.5 16.3 15.4 8-18-75_. 8-22-75___ 8-25-75_ 8-29-75 - 10.8 11.2 11.8 11.6 35.9 32.3 47.9 50.7 59.0 55.0 43.0 GYT GYT GYT GYT GYT YGT YGT YGT GYT GYT GYT GYT GYT YGT YGT YGT GYT GYT GYT GYT GYT YGT YGT YGT MM 111 rootstock 9.9 8-5-75___ 18.1 9.4 8-8-75 - 19.0 8.9 8-11-75_. 18.7 10.9 8-15-75_. 18.2 11.4 8-18-75_. 17.8 12.1 17.8 8-22-75_. 8-25-75.. 31.3 38.0 35.3 51.0 64.7 58.3 52.4 17.6 12.0 12.4 8-29-75_. 16.2 Seedling rootstock 57.7 23.6 8-5-75-18.1 8-8-75__-. 9.5 18.3 8.8 30.1 8-11-75__. 8-15-75_. 8-18-75_. 8-25-75_. 8-29-75_. 8-22-75--. 16.8 17.8 17.4 17.1 9.0 10.5 10.7 11.1 33.8 44.5 48.7 51.6 16.2 15.5 11.2 11.9 W = 43.9 42.0 = green; of 20 fruit. white; Y yellow; T Each value is the average 12 ALABAMA AGRICULTURAL EXPERIMENT STATION the other rootstocks. The fruit exhibited a brown sunburned appearance and was not as attractive. Tree Mortality During the first 11 years of the orchard life (1965-75), a higher percentage of trees died from X. mali, A. mella, C. galactinum, and A. tumefaciens on MM 104 than on MM 106, MM 111, and seedling rootstocks, Table 6. During this 11-year period, 62 percent of trees on MM 104 rootstock died, as compared with 18, 28, and 28 percent on MM 106, MM 111, and seedling rootstocks, respectively. Incidence of black root rot was high in the test orchard and was the major causal organism of tree loss on all rootstock, Table 7. MM 104 rootstock was found to be more susceptible to black root rot than MM 106, MM 111, and seedling rootstocks. Of trees on MM 104 rootstock, 56 percent were lost from black root rot during the 11 growing seasons, 1965-75. Losses on seedling rootstock were 12 percent during the same period. Most tree loss occurred after fruiting began; however, 18 percent of the trees on MM 104 rootstock died during the first 4 years. Apple trees infected with black root rot exhibited sparse, small, off-colored foliage and small, highly-colored fruit. The infected trees died during the season when symptoms appeared or the following year. Trees that had died from black root rot possessed brittle, punky, rotted roots with a black encrustation of X. mali mycelium covering the stump. Trees in such condition snapped off at or slightly below the soil surface. X. mali was isolated only from roots and stumps possessing characteristic symptoms of black root rot. Several X. mali stromata were found on tree stumps. Pathogenicity of all isolates tested were confirmed on apple seedlings. TABLE 6. TREE MORTALITY CAUSED BY ROOT ROTS, BY ROOTSTOCK AND YEAR, PIEDMONT SUBSTATION, 1965-75 Rootstock 1965-67 1968 Pct. MM 104__ 4 1969 Pct. 4 1970 8 Pct. 22 Tree loss 1971 1972 Pct. Pct. Pct. 2 8 1973 1974-75 Total Pct. Pct. Pct. 6 8 62a x MM 1066 . 0 2 0 0 2 2 2 10 18b 28b 2 2 10 6 0 6 0 MM 111 .. 0 14 28b 6 0 2 2 4 0 0 Seedling -. xValues in a column followed by the same letter are not significantly different (Duncan's Multiple Range Test, 5 percent level). PERFORMANCE OF SELECTED APPLE ROOTSTOCK TABLE 7. TREE MORTALITY FROM CERTAIN CAUSAL ORGANISMS , 1 13 PIEDMONT SUBSTATION, 1965-75 Rootstock MM 104----------------- Tree loss Black root rot Oak root rot White root rot Crown gall Pct. Pct. Pct. Pct. ---------- 0 MM 111---------------------28b 0 0 0 ------------------20b 0 Seedling -_ organism: Black root rot (Xylaria mali), oak root rot (Armillaria white root rot (Corticium galactinum), and crown gall (Agrobacterium tumefaciens). ' Values in a column followed by the same letter are not significantly different (Duncan's Multiple Range Test, 5 percent level). MM 106 --------------------------- 56a2 12b 2 6 2 2 'Causal lea), 0 0 8 mel- Incidence of white root rot, oak root rot, and crown gall was slight in the test orchard. During the 11-year period, 2 percent of the trees on MM 104 and 6 percent of the trees on MM 106 rootstock were lost because of oak root rot, and 2 percent of trees on MM 104 and 8 percent on seedling were killed by white root rot. Only 2 percent of the trees on MM 104 rootstock died from crown gall. No trees were lost due to collar rot (Phytophthora cactorum) in this planting, even though MM 106 is reported to be susceptible to it. Woolly Apple Aphid Infestation Seedling rootstocks were significantly more susceptible to woolly apple aphid infestations than MM rootstocks, Table 8. TABLE 8. SUxSCEPTIBILITY OF APPLE ROOTSTOCKS TO THE WOOLLY APPLE APHID, 1 PIEDMONT SUBSTATION Rootstock 1 Rosok MM 104-----MM Trees per rating group 2 2 3 4 Pct. 0 4.3 16.7 4.4 5 Pct. 3.2 0 0 31.1 Raig nfse RaigIfse Av. i.la' 1.Oa 1.2a 2.7b MM Pct. 96.8 95.7 81.0 44.4 Pct. 0 0 2.4 20.0 Pct. 0 0 0 0 Pct. 3.2a l9.1a 106----- Seedling----_-- 111--------- -- 4.3a 'Trees 55.5b were 7 years old when surveyed. 2Rating scale: 1, no infestation or galling; 2, light infestation or galling (only on small feeder 3, medium infestation galling; 4, heavy infestation and 5, heavy infestation galling (located on roots only around a portion of the and galling (located on all roots arounid the roots); Values in a column followed (Duncan's Multiple Range Test, 5 percent level). and tree). aretree); significantly not by the same letter different 14 ALABAMA. AGRICULTURAL EXPERIMENT STATION Most seedling rootstocks were moderately to heavily infested with aphid colonies. Galling was found on lateral roots as well as on small feeder roots. MM rootstocks were lightly infested or galled primarily on the small feeder roots. The MM rootstocks did not differ statistically from each other in resistance to woolly apple aphids. However, MM 111 showed a considerably higher degree of susceptibility (19.1 percent) than MM 104 (3.2 percent) or MM 106 (4.3 percent). Further investigations appear warranted to verify MM rootstock susceptibility to woolly apple aphid. CONCLUSIONS Results of this investigation indicate that MM 106 is the best of the four apple rootstocks tested for the Piedmont Area of central Alabama. Trees on MM 106 had earlier and higher yields, and there was less tree loss than with other rootstocks tested. Rootstock had no influence on bloom date and little effect on fruit maturity. MM 104 rootstock was found to be unsuitable because of its high degree of susceptibility to black root rot. Seedling and MM 111 were unsuitable due to lower yields and susceptibility to woolly apple aphid infestations. Trees on MM 111 rootstocks had sparser and smaller leaves and weaker growth than trees on the other rootstocks tested. This rootstock does not appear adaptable to growing conditions in the Piedmont Area. It was not possible to maintain trees on MM 104, MM 106, and seedling rootstocks short enough to permit pruning and harvesting without the aid of ladders. Additional investigations are needed to find an apple rootstock that will induce earlier and heavier fruiting, possess more disease and insect resistance, and restrict vegetative growth more. Ideal tree height should not exceed 8 to 10 feet for most efficient production. Economy of production and tree size control not only depend on the rootstock used but on scion variety, tree training and pruning, soil type, and cultural management. AUBURN UNIVERSITY With an agricultural research unit in every major soil area, Auburn University serves the Q 0 Q 5 needs of field crop, livestock, forestry, and horticultural producers in each region in Alabama. Every citizen of © 07 Q the State has a stake in this research program, since any advantage from new and more economical ways of producing and handling farm products directly 1 15 benefits the consuming public. Research Unit Identification * 2. 3 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Main Agricultural Experiment Station, Auburn. Tennessee Valley Substation, Belle Mina. Sand Mountain Substation, Crossville. North Alabama Horticulture Substation, Cullman. Upper Coastal Plain Substation, Winfield. Forestry Unit, Fayette County Thorsby Foundation Seed Stocks Farm, Thorsby. Chilton Area Horticulture Substation, Clanton. Forestry Unit, Coosa County. Piedmont Substation, Camp Hill. Plant Breeding Unit, Tallassee. Forestry Unit, Autauga County. Prattville Experiment Field, Prattville. Black Belt Substation, Marion Junction. Tuskegee Experiment Field, Tuskegee. Lower Coastal Plain Substation, Camden. Forestry Unit, Barbour County. Monroeville Experiment Field, Monroeville. Wiregrass Substation, Headland. Brewton Experiment Field, Brewton. Ornamental Horticulture Field Station, Spring Hill. Gulf Cost Substation, Fairhope.