Origin

‘MP-29’ is an interspecific hybrid developed by the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) at Byron, GA, from a cross made in 1994 between ‘Edible Sloe’, an apparent natural plum hybrid thought to include Prunus umbellata Elliot, and an advanced red-leafed peach rootstock selection from the Byron program, SL0014 (P. persica). ‘MP-29’ is reproductively sterile and is useful only as a rootstock.

Description

Unbudded trees of ‘MP-29’ display moderate vigor and a semispreading form. Leaves are red with a morphology intermediate between the plum and peach parents. Flowers are rare with multiple pistils but lacking sepals, petals, and anthers. No fruit have ever been observed on trees of ‘MP-29’. At the Byron location, vegetative budbreak typically coincides with peach cultivars requiring ≈750 h of chilling below 7 °C (45 °F) to break the rest period. ‘MP-29’ is readily propagated using softwood or hardwood cuttings or through tissue culture.

Performance

‘Redhaven’ peach trees budded on ‘MP-29’ and planted in a field trial at the Byron location on an ARR- and PTSL-infested site displayed significantly better resistance to ARR than did those budded on ‘Guardian’ or ‘Sharpe’ (Table 1). Methodology for distinguishing tree mortality resulting from PTSL or ARR has previously been described (Beckman et al., 1998). Susceptibility to ARR is a significant weakness of ‘Guardian’ rootstock (Beckman et al., 1997, 1998). The ARR resistance of ‘MP-29’ was also better than that of ‘Sharpe’, which was released in 2007 to address this deficiency of ‘Guardian’ (Beckman et al., 2008). Southeastern peach growers will generally push up blocks once tree mortality climbs to 50% (Beckman, personal observation). Based on this criterion, had this block been planted on ‘Guardian’, it would have certainly been removed after only eight growing seasons (Table 2) and likely even earlier given establishment losses and other causes during the course of this trial. Although this trial was on a severe PTSL site (based on previous plantings), losses to this cause were minimal during the course of the trial. Unfortunately, a susceptible control had not been included and, as it turned out, all of the other treatments included in this trial evidently possessed good resistance to PTSL (data not shown).

Table 1.

Rootstock influence on cumulative mortality resulting from Armillaria root rot (ARR), peach tree short life (PTSL), and other causes on a severe ARR and PTSL site^z (Byron, 2000–2010).

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Table 2.

Rootstock influence on the time course of tree mortality (%) resulting from Armillaria root rot (ARR) of ‘Redhaven’ peach trees planted on a severe ARR and PTSL site^z (Byron, 2000–2010).

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Unbudded trees of ‘MP-29’ suffered numerically lower losses to ARR than did trees of ‘Sharpe’ and significantly lower losses than did trees of the peach seedling rootstock selection SL1923 in an ongoing Armillaria inoculation trial at the Byron location (Table 3).

Table 3.

Rootstock influence on cumulative mortality resulting from Armillaria root rot (ARR), peach tree short life (PTSL), and other causes on a severe Armillaria infested/inoculated site in central Georgia^z (Byron, 2005–2010).

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‘Majestic’ peach trees budded onto ‘MP-29’ and planted on a severe Armillaria-infested grower site in central Georgia provided significantly better overall survival and significantly lower losses to ARR than did those budded on ‘Guardian’ or ‘Sharpe’ rootstocks after 5 years (Table 4). No trees propagated on either ‘MP-29’ or ‘Guardian’ rootstocks were lost to PTSL. However, trees on ‘Sharpe’ rootstock suffered significant losses to PTSL in this trial.

Table 4.

Rootstock influence on cumulative mortality resulting from Armillaria root rot (ARR), peach tree short life (PTSL), and other causes on a severe Armillaria infested grower site in central Georgia^z (Fort Valley, 2007–2011).

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Similarly, ‘Redhaven’ trees budded on ‘MP-29’ provided resistance to PTSL comparable to those budded on ‘Guardian’ peach seedling rootstock (Table 5), the current industry standard (Beckman and Lang, 2003; Okie et al., 1994), in an ongoing field trial at the Byron location on a site with a known history of PTSL. In contrast, tree losses to PTSL on R97605.1, a peach seedling rootstock selection included in this trial, were significant.

Table 5.

Rootstock influence on cumulative mortality resulting from peach tree short life (PTSL), Armillaria root rot (ARR), and other causes on a severe PTSL infested site in central Georgia^z (Byron, 2005–2011).

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‘MP-29’ displayed no visible galling in a field trial at the Byron location on a site infested with the Southern root-knot nematode (Meloidogyne incognita). The performance of ‘MP-29’ was comparable to ‘Nemaguard’ seedlings, which are regarded as resistant to this nematode (Sharpe, 1974). ‘Lovell’ seedlings, regarded as susceptible to M. incognita (Sharpe, 1974), were severely galled in the same trial. ‘MP-29’ also displayed no visible galling in a field trial in northern Florida on a site infested with M. floridensis. The performance of ‘MP-29’ was comparable to Flordaguard seedlings, which are regarded as resistant to this nematode (Sherman, et al., 1991). ‘Nemaguard’ seedlings, regarded as susceptible to M. floridensis (Sherman et al., 1991), were severely galled in the same trial.

‘Redhaven’ peach trees budded on ‘MP-29’ displayed significantly lower vigor than those budded on ‘Guardian’ and similar to that of trees budded on ‘Sharpe’ (Table 6) in a field trial at the Byron location. The trunk cross-sectional area of trees budded on ‘MP-29’ was ≈75% of those budded on ‘Guardian’ rootstock (similar to those budded on ‘Sharpe’, ≈60% of ‘Guardian’) after 11 growing seasons. Hence, ‘MP-29’ may prove useful as a semidwarf (or tree size-reducing) rootstock for peach.

Table 6.

Rootstock influence on trunk cross-sectional area^z (cm²) of ‘Redhaven’ peach trees planted on a site in central Georgia^y (Byron, 2000–2010).

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Young ‘Redhaven’ trees budded on ‘MP-29’ displayed similar or lower annual yields on a per-tree basis than did those budded on ‘Guardian’ (Table 7). This is probably the result of the lower vigor of peach varieties on ‘MP-29’ rootstock. However, once trees on ‘MP-29’ filled their allotted growing space in this trial (≈4–5 years; Beckman, personal observation), their yield typically exceeded those on ‘Guardian’ rootstock, although these differences were not always significant.

Table 7.

Rootstock influence on annual and cumulative yield (kg/tree) of ‘Redhaven’ peach trees planted on a site in central Georgia^z (Byron, 2000–2010).

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Yield efficiency (yield per unit trunk cross-sectional area) of mature ‘Redhaven’ peach trees budded on ‘MP-29’ was significantly better than those budded on ‘Guardian’ or ‘Sharpe’ (Table 8). This suggests that if trees on ‘MP-29’ were planted at a higher density to compensate for their lower vigor, then per-hectare yields at maturity should equal or possibly exceed those budded on ‘Guardian’.

Table 8.

Rootstock influence on annual and cumulative yield efficiency (kg·cm⁻²) of ‘Redhaven’ peach trees planted on a site in central Georgia^z (Byron, 2000–2010).

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‘Redhaven’ peach trees budded on ‘MP-29’ generally displayed similar average fruit weight as those budded on ‘Guardian’. Average fruit weight of ‘Redhaven’ trees on both ‘MP-29’ and ‘Guardian’ was significantly higher than those budded on ‘Sharpe’ (Table 9). Reduced yield and fruit weight has been a deficiency for peach trees budded on ‘Sharpe’ rootstock, which will likely limit its use despite its generally good disease resistance.

Table 9.

Rootstock influence on fruit weight (g/fruit) of ‘Redhaven’ peach trees planted on a site in central Georgia^z (Byron, 2000–2010).

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Trees budded on ‘MP-29’ and ‘Sharpe’ produced fewer root suckers than did trees budded on ‘Guardian’; although differences were generally not statistically significant (Table 10), all three rootstocks averaging approximately one sucker per year. However, this is based on sucker counts in the fall, which typically only account for those present at the base of trees. Both ‘MP-29’ and ‘Sharpe’ start to produce rootstock suckers out away from the trunk after ≈5–7 years (Beckman, personal observation). These are difficult to account for because they are routinely mowed down mechanically or burned down with post-emergence herbicides during the growing season. Nevertheless, they may pose a risk should growers attempt to chemically mow the orchard floor with a systemic non-selective post-emergent herbicide such as glyphosphate.

Table 10.

Rootstock influence on root suckering (number/tree) of ‘Redhaven’ peach trees planted on a site in central Georgia^z (Byron, 2000–2010).

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‘MP-29’ has been tested for compatibility with a range of peach scions, including ‘Delta’, ‘Faye Elberta’, ‘Fireprince’, ‘Flordaguard’, ‘Cresthaven’, ‘Harvester’, ‘Majestic’, ‘Redglobe’, and ‘Redhaven’, all of which displayed satisfactory compatibility (observation periods range from 3 to 12 years and most are still in progress). Graft unions with peach scions are typically smooth. Tests of graft compatibility of ‘MP-29’ with other Prunus species have been initiated.

Overall, ‘MP-29’ appears to offer a unique combination of broad disease resistance, productivity, and vigor control not found in any other currently available rootstock for peach in the United States. These attributes suggest it for trial in the main peach production areas of the southeast United States and in other production areas suffering similar disease issues.

Availability

A plant patent application has been filed for ‘MP-29’. The Florida Foundation Seed Producers, Inc., Gainesville, FL, will be the licensing agent for ‘MP-29’. Neither the USDA-ARS nor the University of Florida have trees of ‘MP-29’ for distribution. Budwood of ‘MP-29’ has been deposited in the IR-2 Fruit Tree Collection where it is available for research purposes, including development and commercialization of new varieties or rootstocks. Virus-indexed budwood is available from National Virus-Tested Fruit Tree Program, WSU-IAREC, 24106 N. Bunn Road, Prosser, WA 99350–9687.