SLASH PINE FAMILIES IDENTIFIED WITH HIGH RESISTANCE TO FUSIFORM RUST. C. H. Walkinshaw '

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1 SLASH PINE FAMILIES IDENTIFIED WITH HIGH RESISTANCE TO FUSIFORM RUST C. H. Wlkinshw ' Abstrct.--Fusiform rust redily kills slsh pine, Pinus elliottii Engelm. vr. elliottii. When the number of rust-infected trees is high, n investment is ltered nd fewer trees re vilble for hrvest. As infection reches 80 to 100%, the helthy trees pper to be good source of rust resistnce. This method of obtining resistnce from selections of such trees hs been highly productive. In this study, we hve tried n lterntive wy to identify resistnce. We selected rust-free slsh pines with good tree chrcteristics in Ntionl Forests where incidence of rust is low (10-30%). Openpollinted progeny from these trees were inoculted t the Resistnce Screening Center (RSC). Prents tht hd the most resistnt progeny t the RSC were then crossed. Their control-pollinted progeny were tested t the RSC. The resistnce of some of these ws unusully high. Resistnce to fusiform rust is reltively common in individul slsh pines. Keywords: Cronrtium quercuum f.sp. fusiforme, selection for resistnce to rust, Pinus diseses. INTRODUCTION Tree-improvement progrms initilly emphsized growth nd form in the selection of southern pines. When rust hd obviously become problem in the 1940's onwrd, selection procedures imed to identify trees with rust resistnce. Although emphsis is now shifting bck to growth nd form, fusiform rust remins serious problem in slsh pine Pinus elliottii Engelm. vr. elliottii. But the extensive studies of Sluder (1989 A nd B) nd others show tht genes for resistnce to fusiform rust re not difficult to trnsfer nd mny trees crry these genes. Slsh pines tht re resistnt to fusiform rust occur s individuls throughout the rnge. They re generlly identified s symptomtic trees on high-hzrd sites. An exmple of such site is given in Wlkinshw (1987). These rust-resistnt trees hve been useful in forest industry, stte forestry, nd Forest Service progrms. However, mny of the rust-resistnt trees re slow growers. In this study good phenotypes for growth nd form were identified on low-hzrd sites nd rust resistnce ws identified by inocultion. The most resistnt trees were crossed. Dt in this pper show tht these control-pollinted progeny re highly resistnt. Moreover, they strongly suggest tht high resistnce to fusiform rust in slsh pine is reltively common in trees on sites with low rust. Generl Procedure Four steps were followed in this reserch: METHODS ' Plnt Pthologist, USDA, Forest Service, Southern Forest Experiment Sttion, Pineville, Louisin The uthor wishes to express his pprecition to the Coopertive Forest Genetics Reserch Progrm t the University of Florid, Crol H. Young t the RSC, nd J. E. Gtes of the Forest Service for help with this study. 191

2 A totl of 223 slsh pines with good growth nd form were selected from the Ntionl Forests in Region 8. Rust infection in the forests within the vicinity of the selected trees ws pproximtely 30%. Open-pollinted seeds of these 223 pines were tested t Asheville (RSC) nd Gulfport. The trees with the most rust-resistnt progeny nd other modertely resistnt trees were crossed nd the control-pollinted seed were tested t the RSC. Control-pollinted seedlings without swellings fter 6 months were plnted in the Ntionl Forests. Inocultion Designs Open-pollinted seedlots t the RSC in Asheville, North Crolin, were tested in two replictions of three trys of twenty seedlings per fmily. Control-pollinted seedlot tests were replicted three times with three trys of twenty seedlings per fmily. Replictions were one week prt nd freshly prepred inoculum ws used. Trys were rrnged in non-ordered fshion within replictions on the greenhouse benches. The design for inocultions t Gulfport ws identicl to the description given by Wlkinshw nd Bey (1981). These studies were on 211 crosses with forest industry trees. Inocul Selection Severl hundred field isoltes were used to obtin teli from wter ok (Quercus nigr L.) or northern red ok (Q. rubr L.). These provided fusiform-rust inocul for open-pollinted seedlots. In contrst, the inoculum for the control-pollinted fmilies ws from one gll on 10 yer-old slsh pine in Boglus, Louisin. This gll ws selected t rndom nd dopted s the uthor's stndrd for ten yers of screening t Gulfport, Mississippi nd Asheville, North Crolin. To insure tht this isolte provided virulent bsidiospores for infecting the experimentl seedlots, severl resistnt slsh pine seedlots from the Coopertive Forest Genetics Reserch Progrm t the University of Florid were first inoculted. Infection ws: M-707=42%, 52-56=89%, 6-56=70%, =33%, nd =67%. A further test with 27 control-pollinted resistnt trees t Gulfport insured tht the isolte ws pthogenic to wide rnge of slsh pines. Men infection in this test ws 56% nd one-third of the puttive resistnt crosses hd glls on more thn 70% of their seedlings fter 6 months. Inocultions Grvity ("tent"), irstrem, nd wter suspensions were used to deposit bsidiospores on needles nd needle bses of 10-week-old seedlings in flts of soil or in continers. All procedures prlleled those reported previously (Wlkinshw nd Bey 1981, Wlkinshw nd Rolnd 1990). Slsh pine 211 ws extensively inoculted t the RSC nd t Gulfport in n effort to brek down its resistnce. The other highly resistnt slsh pines were inoculted only t the RSC. Observtions Tree nd gll trits were tken in detil but re not given in this pper. Resistnce is defined s the bsence of visible swelling. Outplnted seedlings were selected from those with purple spots on the stems but no swellings. When this type rn out, those without spots nd swellings were plnted. 192

3 RESULTS Resistnce of Fmily 211 Fmily 211 x W hd 23% infection in tent test of 100 seedlings t Gulfport (Tble 1). The men percentge of seedlings with glls for the other Region 8 fmilies in the inocultion ws 80. Results of dditionl tests t Gulfport nd Asheville with fmily 211 x W re given in Tble 1. Note the lrge number of fungl collections tht we used to inoculte the progeny of this slsh pine fmily. The bility to resist so mny rust isoltes ws unique mong Forest Service nd forest industry trees tht we hd tested. Histologicl observtions of fmily 211 tht ws inoculted t Gulfport showed lrge vrition in the mount of cmbium tht ws invded 21 dys fter inocultion. The rnge ws 110 to 925 microns in stem-circumference for 211 crosses, while the susceptible control rnged from 594 to 1225 microns. The highly resistnt University of Florid fmily (M-707) (Bey nd Wlkinshw 1981) verged 256 microns compred to 294 for the 211 crosses. All mesurements of fungl growth were mde on highly virulent rust isolte. Tble 1. Fusiform rust incidence in open-pollinted slsh pine progeny of fmily 211. Inocultion code No. field isoltes in inoculum Percentge of seedlings with glls "Tent" mny (x9) (X12) M-707 nd Rections of fmily 211 were similr to those on Florid tree, (Bey nd Wlkinshw, 1981). In both fmilies mny of the lesions were so smll tht they were not visible to the unided eye. Mny of the successful infections in these two fmilies developed from invded needle trce tissue. Resistnce of Other Select Trees In ddition to fmily 211, severl other highly resistnt slsh pine were identified mong the 223 Region 8 selections. The ones used in the crossing experiment nd their percentge with glls in the open-pollinted progeny were: 211=14%; 224=35%; 331=42%; 311=50%; 304=50%; nd 310=37%. Susceptible check seedlots verged 88% of their seedlings with glls. Infection of the resistnt check ws 68%. Two or three replictions of 60 seedlings were inoculted with 20,000 bsidiospores per ml. Test nd used 9 nd 12 single isoltes, respectively. Susceptible checks hd 65 to 88% of their seedlings with glls. Prllel observtions of resistnt nd susceptible lesion rections on 211 x W showed vrition in fungl growth within nd from the lesion. Periderm formtion ws rre compred to lesions on the highly resistnt Florid trees Resistnce of Crosses Control-pollinted crosses between slsh pine 211 nd eleven slsh pine fmilies tht were being studied t Gulfport were highly resistnt t the RSC (Tble 2). Infection of the crosses ws much lower thn in the resistnt check fmilies. The gll-free survivors t the beginning of the 12th growing seson rnged from 5.0 to 5.7 inches d.b.h. 193

4 Tble 2. Percentge of control-pollinted progeny of slsh pine 211 crosses tht were glled six months fter inocultion.' Cross Glled fter D.b.h. fter 11 yrs. 6 mos. (in.)b 211 x x A x J x JP x H x H x x x x x Two replictions of 60 seedlings were run with ech of two single gll isoltes. Susceptible check verged 70% nd the resistnt check hd 55% infection. b D.b.h. for seedlings with stem purple spots but no glls tht were plnted in the DeSoto Ntionl Forest t 10 x 10 spcing. Progeny of crosses of Region 8 trees hd high resistnce when inoculted t the RSC (Tble 3). Susceptible fmilies 347, 244, 232, nd 214 hd % disesed. The RSC susceptible check hd 85% infection. All crosses of the resistnt trees hd less infection thn the RSC resistnt control seedlot. DISCUSSION Our inocultions show tht high resistnce to fusiform rust exists in slsh pines on low-hzrd sites. Moreover, the resistnce of tree 211 ws effective ginst mny field isoltes of the rust fungus. The infection of progeny of trees 211, 224, 311, 310, 331, nd 304 nd others t the RSC ws unusully low. The fct tht the five susceptible seedlots rnged % is proof tht the inocultion ws effective. As group these control-pollinted trees re the most resistnt ones tht I hve tested in 25 yers. When one exmines the 223 slsh pine fmilies tht were tested t the RSC by the Forest Service, Region 8, it is interesting to discover tht pproximtely 1 tree of 25 good growers hs good resistnce. The other 24 trees re susceptible. This pttern ppers in the good growers selected for potentil rust resistnce in the 1950's (Brber, 1961). Clone of the University of Florid ws one of the good growers with rust resistnce when tested t Gulfport nd Tylor County, Florid. Other good growers in the top 25, such s nd were susceptible. This somewht rndom reltionship between growth nd rust resistnce suggests tht the pressure to select for resistnce ws exerted in prior genertions. The period of co-existence of the rust nd its host (severl million yers) would hve provided mple opportunity for selection. Tble 3. Low infection in control-pollinted crosses of select slsh pines in the USDA Forest Service Region 8 Progrm.' Cross Percentge of seedlings with glls 211 x x x x x x x x x x x 211 Seedlot A x 211 Seedlot B 39 Resistnt check (RSC) 47 Susceptible fmilies RSC 85 Region 8A 100 Region 8B 99 Region 8C 97 Region 8D 97 Three replictions of 60 seedlings were inoculted with single virulent isolte of the rust fungus t concentrtion of 20,000 spores per ml. Microscopy of needle-bse lesions on slsh pine 211 ws interesting. Lesions were unusully smll nd the fungus ws killed before 194

5 periderm ws formed. When glls formed, they were similr in size to susceptible controls. These rections were observed with nine different single-isoltes. The bility of slsh pine to restrict fungl growth to few cells fter penetrtion is common to mny of the University of Florid resistnt fmilies, e.g., Fmily 211 exhibits rections much like these nd other Florid fmilies but is more effective in killing the rust fungus in the outer cortex. CONCLUSIONS Individul rust-resistnt slsh pines commonly occur in the southern forest. These cn be found on both high- nd low-hzrd sites. Asymptomtic trees on high-hzrd sites hve been excellent sources of resistnce, but their growth nd form cn be poor. The lterntive procedure tht ws used in this study led to rust-resistnt selections tht were suitble for plnting in high-rust hzrd res. Gins in growth nd form cn be greter in low-to-moderte-rust res by utilizing the best fmilies even though they re more susceptible to rust. In contrst to the pessimistic view in , the present study, long with the thorough work of E.R. Sluder (1989 A nd B), strongly suggests tht obtining slsh pines with good growth nd form tht lso resist fusiform rust is not difficult (Kinloch nd Wlkinshw 1991). LITERATURE CITED Brber, J.C Growth, crown form, nd fusiform rust resistnce in open-pollinted slsh pine progenies. In Proc. 6th South. For. Tree Improv. Conf. pp Bey, C.F. nd C.H. Wlkinshw Stbility of field resistnt slsh pine to selected isoltes of fusiform rust fungus. In Proc. 16th South. For. Tree Improvement Conf. pp Kinloch, B.B. Jr. nd C.H. Wlkinshw Resistnce to fusiform rust in southern pines: How is it inherited? In Proc. 3rd IUFRO Rusts of Pine Conf. pp Sluder, E.R. 1989A. Fusiform rust in crosses mong resistnt nd susceptible loblolly nd slsh pines. Southern Journl of Applied Forestry 13: Sluder, E.R. 1989B. Gin nd vrition fter two genertions of selection in slsh pine in Georgi. Georgi For. Com. Res. Rept. No. 5. pp 1-9. Wlkinshw, C.H Field nd greenhouse fusiform rust symptoms predict mortlity in progeny field tests. Proc. 19th South. For. Tree Improvement Conf. pp Wlkinshw, C.H. nd C.F. Bey Rection of field-resistnt slsh pines to selected isoltes of Cronrtium quercuum f. sp. fusiforme. Phytopthology 71: Wlkinshw, C.H. nd T.A. Rolnd Incidence nd histology of stem-girdling glls cused by fusiform rust. Phytopthology 80: