Influence of Planting Site and Rootstock on Peach Tree Short-Life Performance of 'Redhaven' Trees

Umedi L. Yadava

Agricultural Research Station, Fort Valley State University, Fort Valley, GA 31030-3298

ABSTRACT. 'Redhaven' peach (Prunus persica (L.) Batsch) trees grafted to eight peach seedling rootstocks, were grown at two sites, one an old peach site with a peach tree short life (PTSL) problem and the other a new site. Trees were evaluated for trunk growth and PTSL-related performance from 1976 to 1979. Planting site and rootstock influenced tree survival, cold injury estimated by trunk cambial browning, bacterial canker (Pseudomonas syringae pv. syringae van Hall) incidence, and trunk growth. Regardless of rootstock type, trees on the PTSL site survived poorly, sustained greater cold or winter injury damage, had more extensive bacterial canker infection, and attained less trunk growth than their counter parts grown on a non-short-life site. After four years, mean tree survival was 90% and 10% for new and PTSL sites, respectively. Tree survival was correlated negatively with cambial browning ® = - 0.83) and the incidence of Pseudomonas canker ® = -0.81), both of which were positively correlated with each other ® = 0.76). Trunk cross sectional area, however, was not correlated with either cold injury or bacterial canker, and was correlated weakly and negatively with tree survival.

A drastic decline in peach tree acreage and reduced orchard longevity in the southeastern United States over the past several decades are partially associated with peach tree short life (PTSL) syndrome which causes premature death of trees (Yadava and Doud, 1980; Ritchie and Clayton, 1981). Accordingly, trees that appeared healthy the previous season suddenly collapse and die during late winter or spring. Partial to complete death of trees above the soil line, greater mortality in light soils on old peach sites, and "sour-sap" odor are some of the salient features of PTSL. The PTSL syndrome results from the interaction of several PTSL-inducing factors, some of which may be acting simultaneously. In the past, to avoid tree losses due to PTSL, growers tried to establish new peach orchards on non-PTSL sites. Due to limited available land area, however, planting on new sites is no longer feasible (Yadava and Doud, 1980). Thus, peach growers are left with no choice but to establish orchards on old peach or PTSL sites. The condition of "soil sickness," resulting primarily from various kinds of phytotoxins in the soil, also has been suspected as an important factor for unthrifty growth and subsequent losses of peach trees (Patrick, 1955; Otto, 1972; Israel et al., 1973; Perkins et al.,1979). Specific replant problems like PTSL syndrome have been associated with physical, chemical, and biological disorders of soil (Traquair, 1984). Reports have also indicated that results for tree growth, cold hardiness, bacterial canker (Pseudomonas syringae pv. syringae van Hall) infection, and peach tree survival were more desirable for those trees grown in non-short-life (NPSL) soils than in soils from old PTSL sites(Weaver et al., 1974; Ritchie and Clayton, 1981; Yadava, 1991).

Rootstock plays an important role in scion physiology, and has been implicated in PTSL development, which is often recognized as a rootstock problem (Dozier et al., 1984; Rom et al., 1985; Yadava and Doud, 1989).To alleviate further tree losses due to PTSL, the influence of different rootstocks in new and old peach sites on tree survival needs study. Although it is unlikely that any particular rootstock genotype possesses all desirable qualities necessary for growing under variable "soil sickness" or similar conditions, there is an abundance of peach germplasm available from which to choose superior and more suitable rootstocks (Otto, 1972;Chaplin and Schneider, 1974; Yadava and Doud, 1978a; Layne, 1987;Yadava and Doud, 1989; Yadava, 1992). Therefore, the purpose of this study was to examine the influence of planting site and peach seedling rootstocks on scion susceptibility to PTSL as assessed by trunk growth, tree injury caused by cold stress and bacterial canker, and tree survival. A report on preliminary observations before the completion of the 12-year investigation, was published previously (Yadava and Doud, 1978a).

MATERIALS AND METHODS

Planting Sites. Two sites 500 m apart were selected at the USDA Southeastern Fruit and Tree Nut Research Station, Byron, Georgia. The soil was a Faceville fine sandy loam. The non-peach-tree-short-life (NPSL) site had not been planted to peach trees for at least 20 years prior to this planting. The soil was pre-plant fumigated with methyl bromide at the rate of 460kg ha^-1 to control nematodes. The "10-point program" for orchard maintenance and the short-life management (Brittain and Miller, 1978) was followed for site preparation and post-plant orchard care. To control nematode population growth, the orchard was post-plant fumigated in 1978 with 1, 2-dibromo-3-chloropropane at the rate of 40 kg _ ha^-l. The PTSL or old peach planting site, which because of frequently occurring premature tree mortalities, was repeatedly planted in peaches for many years prior to this planting. This site was not pre- or post-plant fumigated.

Plant Material. Each site contained 192 'Redhaven' peach [Prunuspersica (L.) Batsch] trees, propagated by the North Carolina Agricultural Research Service, in cooperation with the North Carolina Foundation Seed Producers, Inc., by bud-grafting on eight different peach seedling rootstocks [Halford, Harrow 208, Lovell, NA-8 (North Carolina mountain natural selection), Nemaguard, RL-NRL-4 (a red leaf Nemaguard selection), Siberian C, and 152-AI-2 (a North Carolina long lived selection resistant to some nematode species)]. Three of the rootstocks (NA-8, RL-NRL-4, and 152-AI-2) came from a peach rootstock improvement program for cold hardiness and PTSL by C. N. Clayton (North Carolina State University).

Planting. One-year-old trees were planted during February 1976, 4.5 m apart in rows spaced 6 m using a randomized complete block design with 24 trees per rootstock in 4 and 6 replications on NPSL and PTSL sites, respectively. Weed control was achieved through recommended herbicide applications in 2.5 m wide strips in tree rows, while native grass was allowed to cover the area between the rows. Other cultural practices such as tree training, pruning, and fertilizer application were those conventionally used in the middle Georgia area.

Data Collection. To determine cold hardiness and assess the extent of tissue damage caused by freezing temperature, trees were examined each March for trunk cambium discoloration due to cold injury. Simultaneously with cold injury evaluation, trees also were rated visually for Pseudomonas cankers. Observations for cold injury were made using a 1 to 9 rating scale (Yadava et al., 1984) where tissue damage assessed 1 = no browning, healthy tissue with incremental progresses in tissue browning and injury until it reached 9 = all tissues completely brown, bark separated from wood, and tree was dead or dying. Trees reaching 7 or higher ratings sustained injury beyond recovery. The rating of 1 for bacterial canker indicated healthy tree with no sign of canker. As the canker infection progressed from few twigs to many, to branches, to limbs, and to the trunk, damaging these tissues partially or fully, the ratings went up to 9 when the entire tree was killed. To distinguish between damages caused by freeze injury and bacterial canker (Pseudomonas syringae), we used the technique reported by Yadava et al. (1984); cold injury usually caused uniform cambial browning progressing in basipetal fashion over large areas around the tree trunk, while tissue browning from Pseudomonas infection was restricted to elongated canker streaks with definite margins running basipetally. Trunk tissue discoloration caused by cold injury or Pseudomonas cankers never extended below the soil line. Tree growth, measured a strunk circumference at 30 cm above ground, was recorded each December. Trees which were killed, damaged critically, or injured severely by PTSL causing factors (more than 50% loss of fruit bearing surface) were considered dead trees. Percent tree survival was also calculated.

Data Analysis. Tree survival observations were analyzed statistically by year with analysis of variance using General Linear Model (GLM) procedure of SAS (SAS Institute, Cary, North Carolina, USA); whereas, data for other parameters were pooled across years to compare the planting sites and rootstock effects. Means were separated by Duncan's multiple range test (p = 0.05), and Pearson correlation coefficients were calculated to determine the relationship among various parameters. In the graphic data presentation, values for standard errors (p = 0.05) of the means were presented.

RESULTS AND DISCUSSION

Tree Survival. Peach tree survival was greater in the NPSL site than in the PTSL site beginning in 1976 (Figure 1A). Differences in tree survival among the two sites increased over time. The orchard on the PTSL site was removed at the end of 1979 when less than 10% of the trees were alive. In contrast, after four growing seasons, more than 90% of the trees still survived on the NPSL site. Differences due to planting sites were highly significant (Table 1). Due to repeated replantings of peach trees on the PTSL site, the soil may have supported dense populations of detrimental nematodes and other microorganisms (Nyczepir et al., 1985) or become too rich in substances phytotoxic to peach replants (Patrick, 1955; Otto, 1972; Perkins et al., 1979). Thus, most trees, including those on such desirable rootstocks as Lovell and Halford which are partially tolerant to PTSL, succumbed to the PTSL syndrome within four years.

Trees on Lovell rootstock survived better than those on several other rootstocks, particularly Siberian C and NRL4, both of which had no live trees on the site by spring 1979 (Table 1). Compared to other rootstocks, trees on Siberian C and NRL-4 had the poorest survival. Such poor performance of trees on Siberian C also has been reported by several workers from the southeastern United States (Dozier et al., 1984; Rom et al., 1987; Yadava and Doud, 1978a, 1989). Tree survival was correlated negatively with trunk carnbial browning ® = -0.83), Pseudomonas canker ® =_0.81), and trunk measurements ® = - 0.26). These relationships indicate that increased susceptibility to cold injury and bacterial canker contributed significantly to tree death.

Cold Injury. Cold injury in the cambial region was affected significantly by planting site and rootstock; the differences were consistent over the entire period of this investigation (Table 1, Figure 1B). Trees on the same rootstocks experienced greater cold injury when grown on PTSL site than on non-PTSL site. This result demonstrated that PTSL-causing factors contained in the PTSL site soil weakened trees, making them susceptible to cold injury. These results support earlier studies concerning the influence of PTSL site on cold hardiness and tree survival (Yadava, 1988,1991; Yadava and Doud, 1978a, 1978b, 1980). Trees growing on SiberianC and NRL-4 rootstock, invariably sustained more cold injury than those on other rootstocks (Table 1). Lovell and Halford rootstocks when grown on the PTSL site, imparted significantly more cold hardiness (lower values for cambial browning) to the scion than did other rootstocks. As reported earlier by Yadava and Doud (1978b, 1992) and Yadava (1988), peach scions grafted to Siberian C and NRL-4 rootstocks, unlike the ungrafted seedling trees of Siberian C, developed thick and spongy bark rendering this and surrounding tissues vulnerable to cold injury during fluctuating winter temperatures. Such an undesirable response of 'Redhaven' peach scion on Siberian C rootstock may suggest some form of incompatibility. Ashworth et al. (1983) suggested that tightly packed cells facilitate supercooling of tissues and prevent cold injury, lending support to the findings of this study. Thus, greater cold injury on trees with thick and spongy bark on Siberian C and NRL4 rootstocks may have resulted from their higher vulnerability to fluctuating temperatures than on other rootstocks. Similar results on vulnerability to cold injury of trees grafted to rootstocks like Siberian C, have been reported from the southeastern United States (Chaplin and Schneider, 1974; Dozier et al., 1984; Rom et al., 1985; Yadava and Doud, 1978a; 1989; Yadava, 1992; Yadava et al., 1978). Layne et al.(1977) and Layne (1987), however, found Siberian C to be hardier than other rootstocks tested in Ontario, Canada. Furthermore, this rootstock is not only root hardy but increases scion hardiness under northern conditions. Thus, it appears to be possible that in the southeastern United States, Siberian C when used as a rootstock for peach may reduce the physiodormancy requirements of the scion cultivar, causing early deacclimation and scion injury, although the rootstock itself remains hardy and is not injured by the cold.

Cold injury estimated by trunk cambial browning was correlated directly with the damage caused by bacterial canker ® = 0.76). The damages due to cold injury and Pseudomonas canker were correlated negatively with tree survival, but there was no significant association with trunk circumference. These data indicate that trees sustaining greater cold or winter injury were more likely to be infected by Pseudomonas s)!ringae and develop cankers, or vice versa, and die of PTSL syndrome.

Bacterial Canke/: Data indicated that both the planting site as well as rootstock influenced significantly the development of Pseudomonas syringae infection and ensuing canker damages on peach trees (Table 1, Figure 1C). The effects of the planting site were greater than that imparted by the rootstock type; trees were infected more frequently and experienced greater tissue damage on the PTSL site than their counterparts on non-PTSL site. These results support an earlier report by Weaver et al. (1974), where rootstock significantly influenced the development of Pseudomonas canker. Trees grafted to Siberian C and NRL-4 rootstocks on both planting sites consistently had greater canker damages than trees grafted to Lovell and Halford rootstocks (Table 1). In general, trees killed by the PTSL syndrome exhibited a typical "sour-sap" odor often associated with cankerous tissues (Weaver et al., 1974; Ritchie and Clayton, 1981; Yadava and Doud, 1980, 1989). The incidence of bacterial canker was correlated positively with cambial browning, negatively with tree survival, but was not associated with trunk growth.

Trunk Growth. Both planting site and rootstock type influenced tree growth significantly as measured by trunk cross-sectional area (Table 1, Figure 1D). Trees planted on the PTSL site grew slower and had smaller trunk area than did their counterparts in the non-PTSL soil. Similar differences in tree growth due to the effects of planting site have been reported by other researchers (Israel et al., 1973; Yadava and Doud, 1978a; Traquair, 1984). Although differences due to rootstock varied, trees on Lovell rootstock had significantly larger trunks than trees on Siberian C, regardless of the planting site (Table 1). These data partially support the findings of Layne et al. (1976) and Zehr et al. (1976), and similar results were reported from a regional rootstock project in the southeastern United States (Dozier et al., 1984; Rom et al., 1985). Trunk cross-sectional area was correlated negatively ® = - 0.26, p = 0.05) with tree survival but was not related to cold injury (cambial browning) or bacterial canker ratings. It is difficult to explain the weak correlation of trunk growth with survival criteria. This result may not be surprising since trees appear normal the season before they die.

CONCLUSIONS

Planting site and rootstock significantly influenced PI SL performance of 'Redhaven' peach Lees. The effect of planting site was greater than the rootstock effect because tree survival was drastically reduced on the PTSL SITE (< 10%) in just four years compared to the 12 years required to reach a comparable level on the same rootstocks growing on the non-PTSL site(Yadava, 1992). Trees on Lovell survived better than on other rootstocks even under the best conditions suitable for PTSL development.

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