(gca)in practice, however, ... ic gf rhe processes of pollination (pollen grain germination, pollen...

David F. Van ~ a v e r b e k & /

Abstract.--In a breeding program begun i n 1970, 7 s e l e c t t e s t e r Crees are be ing used t o produce progenies f o r evaluating 43 Scots p ine seed orchard s e l e c t i o n s of provenance o r i g i n and t o provide m a t e r i a l for recurrent s e l e c t i o n . Average cone s u r v i v a l has been 50 percent (range 36 t o 60) and number of sound seeds p e r cone 6 ( range 3 t o 1 2 ) over a 5-year pe r iod . Prel iminary ana lyses i n d i c a t e 76 and 58 percent o f the total varia t ion f o r cone s u r v i v a l and number of seed per cone, respectively, is a t t r i b u t a b l e t o the ovu la t e parents, General combin- ing a b i l i t y (GCA) e f f e c t s appear l a r g e r than s p e c i f i c combining a b i l i t y (SCA) e f f e c t s among testers. GCA e f f e c t s w e r e not d i f f e r e n t except for one tester i n cone s u r v i v a l . SCA effects i n d i c a t e wide v a r i a b i l i t y . Data suggest s u f f i c i e n t v a r i a t i o n i n cone survival and seed per cone for effective s e l e c t i o n ; and importance of choosing spec i f ic combina- tions of parents,

: Scots pine , Pinus breeding program, testes-cross, cone and seed production.

In theory, the genetic evaluation of clonal. seed orchard s e l e c t i o n s , through breeding and progeny testing, should precede the es tab l i shment of t h e sesd orchard. In practice, however, progeny t e s t i n g of t h e s e l e c t e d paren t ccee9 is cs~.resaly delayed u n t i E ramets o f the selected ortets produce ovu la t e s c r o S i l i i n the seed orchard, T h i s i s due, p r h a r i l y , t o the expense, d t f f i c .uLtys and inconvenience of breeding l a r g e , widely separa ted parent epees . i n t e r field conditions.

Tn the present program w e initiated our "D~eedng p r o g r m cancu r r en t ly wj-eh ehe esrablishnnent of a product ion seed orchard (Van Haverbeke, BagLey arid Bensan 1943, Van Haverbeke 1974) ,

THE BASE POPULATION

Ln 195M a r eg iona l e f f o r t was begun to Improve the gua l l t y of Scots p ine (PrL "71JS - -- L . ) p l an t ing s tock throughout t h e northcentral reg ion of the United States (Wright and B u l l 1963, Wright et al. 1966) . I n 1962 person- 11eL s f the Rocky Mountain Forest and k n g e Experi~ent Station, U . S B D , A , Fores t Service, and the Department of Hsrtieu%:ure and Forestry, University of 24ebraska -- in, cooperat ion w i th Wright -- established a Scots p ine provenance test plantation near Plattsmouth, Nebraska, containing over 1,000 seedlings iuom 36 stand o r i g i n s across Europe and Asia (Read 1971), -- -- --- --- - l/l?aper presented at Tenth Central States Fores t Tree Improvement Conference, -- . ? ~ ~ d u e University, West Lafayette, Indiana, S e p k e ~ a b e r 21-23, 1976.

-/?:search Forester, Rocky Mountain Forest and Range Experiment S t a t i on , - ? . - v ~ k ~ s ~ ~ a t r y - Sciences Laboratory, University of Nebraska, Lincoln, 68503.

T13E BREEDING POPULATION

In ;47:C), whec the provenance? p l a n t a t i o n was 8 years o l d , e<~cl-r r rce t a e2

rar-ed for f o l i a g e color, Salance, 'oliage density, form, .'taper, _3 1 e -r-

t i o n , and stem straightness -- all d e s i r a b l e Chriscms and s cn2men tAi - p

c;~a:d.acteristi~s. Forty-three s u p e r i s r phenotypes were seieeted as cPsl , -sc~::-- i n g p o p u l a t i o n f o r the development sf an improved strain o f Scots pin-2e

Secause winter foliage c o l o r is an i n p o r t a n t Chrisrmas 2nd orna-iaei.l-;-,~2: Zree cha rac t e r i s t i c , most of our superior selectj-O~S ~ 3 1 ~ f r3m p r 0 v ~ n 1 ~ 3 ' t ~ s h che southern p o r t i o n s f t h e species range: from provenances 213, 2 L 5 , 240, 239, 235, 203 , 557, 556, 554, 2 4 2 , 551, 2 4 3 , 228, 261, and 264 (Kesu 1971)--- sources noi;eG for t k i r green t o blue-green w in t e r f o l i a g e coior, P Y ~ : - J ~ L - ~ - ~ C L -4 ,- n - /:i~, 230, 557, 556, and 554, however, do not develop t h i s d s s i r a b l e w i x - f o l i a g e color in 3Iichigan o r ?ennsylvani;.?l Eighteeri oF the 36 ;c:.~2;..2-<-6:~

are represented among c h e se lec t ions , Numbers of selections p e r provcqanrc ragged from one k o s i x s

The prolrr.nance P e s t crces were rhe same age, g r m i n g under - ~ - c ~ r ; : i ; t ~ ~ ~ , u r k i b n ~ s p a c i n g and s i t e conditions ; tile origins were ralzdt1a1e-i rrsss gnec :.r : - : I : r t h e p l a n t a t i o n t o ~ e r m i c valid analysis of t h e i r performances,

i n i t i a t e d 2 f u l l - s i b progeny test by rnaking contrslled nzatir12" +-I a se lec ted trees i n t he provenance test because: (I) the s e l e r t c d , I - ( " . _ ~

were concentrated i z r one convenient I s c a t i o n , (2) Lke ease t 2 f makiLp C O L ~ -

t r o l l e d crQsses OE trees 8 years of age, and (3 ) severak szlected t r * a t a s i i--:i

;arod~rcing strobili = thie reasoned that severa l y c a r s coul i i be ea<;~ea;i. bx: 71- 1 , .. , c g n t r s l i e d pollinations on t h e paren t trees, rsthc2r than wa- i t ing for r A n e k s i n a g r a f t e d seed orchard t o p roduce s t r o b i l i .

Aisc?, t h e relatfve1:- un i fo rm environment of the test s i t e m a d s it i-~;:e~:> t h?r irhe phenotypic expressions of the selected trees ' cbiaracteriss"ics -- lxrr

f a i r l y accuraee manifes~ation of their genotypic po~entiai, Par t h e 2 2 4 L - .."b redsons we e l s o dr=cidec; co e ~ t a b l l s f ~ a c l o n a l seed orchard of the S C ' P ~ ~ + : ~ - - - - ~

concurrent 1.. w i t h ~I-ae i n i t z a t icg-r. o f t h e b r e e d i n g program,

BREEDISG SCWEME

rTq North C~rcsl ina S t a t e @esiz-n~ 11 (Tester-Cr~ss) was dciopted ia O U "

; ~ r ~ g r a r n to detl--;-mine t b s gerzt5ti.z y~a lue 3f the s e l e c ~ e d trees. This Sis2l-t 53 scheriie is considered to be one 3f thc simplest and mcst f l e x i b l ? rrot;r,ix? i ~ r t e s t i n g 2rogen-y from e o n t r o i l e d pol l i reat ions (Zilbcl et ale j-37 -; * L p r o v i d e s information about general combining a b i l i t y (GCA) , gix-~es 2 n ~ d j u - r e aC

* - * s ~ e c l l i c combining a b i l i t y (SCA) , and can give i n fom~a t i . sn 0x1 i;nbr 2ed ~ r i ;

e f f ec t s* T h i s scheme requires t he use of four t o s i x of t hc select treLr** designated as testers , ~ r h k c h are c rossed wick a l l of he se l cz t t rees ,

T h i s scheme y i e l d s a satisfactory estimate of parental breeding value, b ~ i t has been c r i t i c i z e d f o r use i n r e l a t i v e l y small programs because the progeny population produced f o r r ecu r r en t selection is r e s t r i c t e d by too Iew unrelated families (Zobel et al. 1 9 7 2 ) . There can be no more unrelated crosses than the number of t e s t e r s used. How~ver , in view of the extreme gene'ric d i v e r s i t y of our breeding material, and limited po l l en product ion on oil-=. relatively young select t r e e s , w e conclclded i t was b e s t suited f o r our p c;4c~:amjrbs

Seven of t h e s e l e c t trees which produced abundant pollen, and represen ted germ p l a s m from six provenances across an east-west transect of the spec i e s range (number 239, 556, 557, 2 4 2 , 243 and 264) were s e l e c t e d as the t e s t e r s .

Wi. used the "Mini ~ a g " technique (Gerhold 1968) and p l a s t i c b o t t l e oaJ!-inators (Barnhart 1976) for making our cont ro l led pollinations.

We realized our s u p e r i o r trees were q u i t e young when s e l e c t e d . Thus , rl-ir presence and q u a n t i t y of s t r o b i l i were l i m i t i n g factors early i n the ~rt2gram---precluding i n i t i a t i o n o f a breeding scheme such as one sf the .iLsiLe! plans. About 10 of the selected trees have yet t o produce any, or cacwpil, s c r o b i l i , i n c l u d i n g one o f the tester trees, to warrant breeding them. Since one o f our major objectives was the establishment of a production seed 6-;hard as qu i ck ly as p o s s i b l e , we m y have to eliminate the trees selected a c i g i n a l l y that are still i n f e r t i l e , and replace them i n t h e breeding program ;-it;; f e r t i l e trees that w e r e less desirable i n the o r i g i n a l s e l e c t i o n process .

S t r sb5-Li Production

Ti-~e nuniber o f select trees producing ovulate s t r o b i l i has increased from 23 to 33 during t h e past 7 years, with indications t h a t add i r iona l t r e e s w i l l be p~odi~ci l r rg o w l a t e scrobili, and pollen, as they cont inue t o mature I ) .

Gcme Survival

Cone surviva% dur ing the past 5 years has averaged 50 percent, w i t h a s n g c ot 35 to 60 percent (Table 1). Brown (1971) r e p o r t e d 65 percent cone sdi->~jval in England w i t h f r e s h p o l l e n , as we also use , bu t only 30 to 65 1;ercen.t su rv iva l with scared po l l en , We have not investigated the causes of Qur cone Josses, b u t believe many are l o s t during t h e f irst year between pel-l i l l a t ion and fertilization. Brovrn (1971) stated tha t f i n a l cone and seer? y + e l d s f r o n c o n t r o l - p o l l h a t e d ercssses may be inf lueneed by breakdown of any ~ : i c G F rhe processes of pollination (pollen gra in germination, pollen tube grot-ch) , ?ert-ill z a t i o n , embryo Bevelcspment , or pptemidmre abscission of marur- 1qg cones*

We have a t ea ined averages of about 6 and 4 seeds per cone in controk- and spen-pol l ina ted cones, respectively (Table I )* Yields from our controlled po! i ina t ious i n terms of sound seed per cone, have not been impressive, but have been similar i n m g n i t u d e to yields reported by Johnson e t %Is (1953)

and B cone 3ich-j-

rown (1971). Gerhold lias obtained average yields of 1.C tc I 4 seeds p e r in different years on the same Scots pine t r e e s cross-pollinated i n

36 gall. -

Our cones are processed and seed extracted ss d e s c r i b e d by Van i-kaverbeke ( i n press) ,

Zaseecs and Disease - - --- ---

Average seed y i e l d s p e r cone rose from about 3 in 2931 to n e a r l y 12 in q r,-i.t i r : ~ , ?laen decreased sha rp ly to about 3 by 1945 (Table 1). lii'e believe t h i s thsrease w a s l a rge ly a t t r i b u t a b l e to a dramatic build-rmp o f t h e kcaf foo ted ?ine seedbug ( corccb1u.1) (524") (EbeL ee: ab, 197% ). T h i s s u c k i n g incc:ct feeds upon the developing p i n e cones, kt moves f r m ,me c lus te r to -one c lus te r , puncturing the cone scales w f t h needle-like ;i:.idthpa.-ts, and '2xtr2iecing nutrients from i n d i v i d u a l seeds,

The selected. trees were treated in s p r i n g 1476 wi th the grariz.lar i'cm! of the svstemic insecticide caarbsf~ran (common name; Furadz-1, t r z d e name 107' 0 at rates of 170 and 227 gm. p e r inch o h s t e x d i a r w t - r a t breast h e i g h t . The granules were raked i n t o the soil 0 1 1 t t3 the i l r ip- l i lac o f the tree crowns, Results will be evaluated in fall 1976.

S k i i l i n g and NicsPlo1I.s (1974) repor ted se r ious losses of Scot:, p i n e b~ Christnas tree growers in the north- central states due to brgwn spot needle

-7 c i sease , caused by the fungus Sc-lrrhiz acicola (Dear".) S iggiars - i n e y r t~p t~ rcc r t that t he shoot-needled varieties o f "'SPanisklH' and ''~rerpei.l% "~een" Sc;lts jrixle are more suscepc ih l e to the disease than the long--needled va r i e t i e s . iic have ie tected brown s p o t on cine of our select trees- A shor t -need led t ree nf :2paEish o r i g i n from source 245*

Co?e at2d seed data from t h i s b reed ing program -an noc y e t ie lirectry - : ~ s t e i ! f o r s i g n i f i c a n c e because of Lack s f a p r o p e r error ten9 (nc repaica-- - , - " c r A d f s e l e c t t r e ~ s as in a c l o n a l see& ~ r z h a r d , 2 ~ 6 P - ~ c ~ ~ p t c t * ? r e c e t i t l ~ n n & - rs-osses in 31% years) . While these data rnust Re ~o~alaaret"a"c3relirninary .I*-@ ij-'_ewed \.rich caut ion (Schruer~ et zle 1975) some genet r c trenGs are a p p a r e ~ t 7%-

1 2 ~ c ~ i ~ L a t e (female) parents acc63i~;f~ted for 76 and 53 percens o f the t o t a l J t r a ~ t i c i r ~ i r i p e r c e n t cone survival and number o f sound kCcl;"s 9c-r C G ~ ~ C ~

v ~ ~ s L ~ 3 , c a - - 7 - 2 OfiLy 0.7 and 6 p e r c e n t of t h e variation fcr thc*>d c:~i~eail ~$trs bgL 2 ~ t t r i b u t e d to t h e staminate (male) pare~;ts , T h i s i s no t surF~ising s i n c e ! i j r h c !~~-r~~cters are primarily maternal furzetions, especial ly co:se ~ i ~ u v i v a l - K;ir_r-f& t and Gerh01d (1973) and karr l 'a l tee t ale (1975) forrnd t h d ~ the ,~-k_ember

2 1 i e d seeds per cone, as well as seed w e i g h t , was influencca by both 2 1: s_igs_rs, qut was affected to a much larger ex tenc by the oi:ula.tc : : ;>alcnt*

0 - r u l a t e trees e p p e a r to d i f f e r widePv in t h e i r inherent 2 3 i l i t y to c a r r y - -n_s maturity and to produce v iab le seed ("Tables 2 and 3) a E r o w n 9197%) z i s o reparted that cone losses var ied great3y among c lones ?i;.er when on? ,?32 lerl Goarree and one i s o l a t i o n p rocedure ::wee used . R? aand F ~ ) r s i r ~ e l h (L944) fur lhe- r e p o r t e d rhaz the t o t a l r-zumber o f seeds per cone ~ h s s F e if:': to ezch la -_ . L S L ~ , i_15_,i-:l ,> c lone in S c o ~ s ; pine and v a r ~ e d g r e a t l y a m o q e l ~ ~ n e s , .AbI.t,he~a~~i--~ the

Table 2,--Rankinn of s e l e c t Scots ~ i n e t r e e s on b a s i s of combined performances of mean percent cone s u r v i v a l and number of sound seeds per cone. ( r = 0.481).

Se lec t Mean percent Mean seeds t r e e cone su rv iva l per cone

" Se lec t t r e e s used a s t e s t e r (pol1en)parents.

Table 3.--Mean values of percent cone survival and nunnber of seeds per cone among t e s t e r crosses.

t e s t e r s : 239 242 243 264 556 557 : Totals

I/ F i r s t value shown is f o r percent cone survival; value in parenthesis - i s f o r number of sound seeds p e r cone.

specific reasons for this v a r i a t i o n , de t ec t ed also i n this s tudy , are not f u l l y i d e n t i f i e d , i t can very probably be a t t r i b u t e d first t o the Inherent a b i l i t y s f particular genotypes t o produce canes and seed, and second, to t h e interaction of t he se extremely d ive r se genotypes w i t h t h e local environ- ment. Var i a t i on may also be due t o s u s c e p t i b i l i t y of ovu la t e parents t o seedbugs. The two c h a r a c t e r s i n v e s t i g a t e d i n t h i s study--percent cone survival and n u d e r of sound seeds per cone--showed a low correlation QOa48%>*

Contrary t o t h e f indings of Bram ( l 9 7 1 ) , our c o n t r s l - p o l l i n a t e d cones are yielding s l i g h t l y more seed p e r cone than open-pol l inated cones 6ron the saxe trees, This could be a t t r i b u t e d t o inadequate pol len product ion from so f e w trees, o r such d i v e r s e o r i g i n s , i n a non-indigenous environment,

While our seed yields seem Pow, they are t h e residual seeds l e f t a f ter f l o t a t i o n i n petroleum e t h e r (Mrugman and Jenkinson 1975). A germination test s f three l o t s af c o n t r s l - and spen-pol l inated seed yielded percentages o f 92 (L--261-3 x 1-243-11, 92 (B-554-4, 0 .P . ) and 79 (E-556-2, O . P , ) , These data suggest that sound seeds were e x t r a c t e d (Table 4 ) *

Estimates of combining a b i l i t y a r e t r a d i t i o n a l l y der ived from progeny performances rather than p a r e n t a l per fomances a s w e have donen There is genst ic v a r i a t i o n i n cone s u r v i v a l and seed product ion however, and estimates were computed t o f u r t h e r i n t e r p r e t g e n e t i c e f f e c t s , Est imates based on the performances s f progenies der ived from these c ros se s will be made a t an appropriate t ime i n t h e f u t u r e .

Among the t e s t e r t rees , genera l connbining ability (GCA) effects appear to be somewhat l a r g e r than spec i f ic combining a b i l i t y (SCA) effects f o r 50th variables. GCA e f f e c t s do not appear ts be g r e a t l y d i f fe ren t along testers except for poor cone s u r v i v a l f o r tree 6-557-1 (Table 5) ( G r i f f i n g 2.956).

Estimates of SCA e f f e c t s , however, show wide v a r i a b i l i t y among t he trees far percent cone s u r v i v a l , bu t are r e l a t i v e l y uniform for number of seeds p e r cone (Table S ) , " T h i s probably i n d i c a t e s t h a t c e r t a i n pairings are more compatible than o t h e r s ,

Estimates mong t h e tester trees sugges t t h a t reciprocal effects are large, especially with regard t o cane s u r v i v a l , i n crosses involving 6-557-1 ( ~ a b 8 e 6) ( G r i f f i n g 1956) . This indicates t h a t the reciprocal crosses a r e not performing s h i l a r l y ; perhaps care should be taken i n the choice o f seed parent f o r particular crosses,

Our select trees were r e l ea sed from competitive influences by removal sf adjacent trees an a11 sides. However, some crowding--leading t o shading of branches, l o s s of v i g o r , and u l t i w t e l o s s of csnes--could have influenced cone survival i n certain p o r t i o n s o r sides of t h e crowns. While the spatial arrangeaent of the var ious matings w i t h i n the c r s m s was presumed t o be random, crowding effects could exp la in , i n p a r t , the large reciprocal effects shown i n Tab le 6 , Brown (19711, f o r example, found cone drop on the north s i d e of the crowns sf Scots p ine was almost double t h e drop on the south s i d e -

Table 4.--Sound control-pollinated seeds produced in Scots pine interprovenance breeding program after 5 harvests (1971-1975).

Ovulate : Tester parents parents : E L L J G

239 242 243 G M 264 556 557 . 2 557

1 1 1 L 1 2

- -- - ------- -- --- ----- l! ;;C.- = general combining a b i l i t y ; SCA = s p e c i f i c combining ability

l/ i ' i xs t value shown i s f o r percent cone su rv iva l ; value i n parenthesis i s -- for ~amber of sound seeds p e r cone.

--- --------*a- --- m---- - - - - elect- :--- Tester t r e e s -- -

a>-i,i: :

- - --- ----- -- -.=---"-- ---- '/ RLrst value shocm is f o r percent cone survival ; value i n parenthesis i s --

l o r number of sound seeds per cone.

These d a t a i n d i c a t e the importance of choosing t h e specif ic parents i n a combination, a d then t h e s e l e c t i o n of ~ghich of t hose pa ren t s t o use a s t h e f e n a l e t o a t t a h maximm cone s u r v i v a l * For example, no te c ros se s of 6 5 5 6 - t o L-242-1 and 1-243-1 for s p e c i f i c and r e c i p r o c a l e f f e c t s . These da t . a l s o suggest gene t i c v a r i a t i o n m o m g the sources i s serffhi ient f o r s e l e c t i o n t o show progress , e s p e c i a l l y w i t h respect to cone s u r v i v a l * Less v a r i a t i o n e x i s t s f o r nurnber of seeds per cone, but the range i n values i n d i c a t e s t h a t some progress could also be made,

Our goals ine lude : ( I ) evaluation of the s e l e c t t r e e s through progeny t e s t i n g , (2) r e c u r r e n t s e l e c t i o n from w i t h i n these progenies, and (3) the5r conversion t o e i t h e r a 2 improved seedl ing seed orchard or the establishment of a second product ion c l o n a l seed archard* Zeaser ($976) detected desirable combinlations of t ra i t s (he igh t , w in t e r f o l i a g e co to r , needle h n g t h , crook and sweep) i n f a m i l y progenies from i n t e r - and i n t r a - v a r i e t a l Sco t s pine matings,

We a n t i c i p a t e d completing a s u b s t a n t i a l nmber of the required 'tmtings by s p r i n g 1976 and i n i t i a t i n g a progeny test w i t h as many s f the t r e e s as we have complete sets of c ros se s i n s p r i n g 1978, W e expect t h i s nuniber to i nc lude about 25 t o 30 t r e e s , o r 1 9 7 t o 210 separate progeny families.

Real iz ing t h a t our program is not large and t h a t the tester-cross program y i e l d s a r e l a t i v e l y small number of un re l a t ed f a m i l i e s , we made about a dozen single-pair n a t i n g s i n s p r i n g 1976, u t i l i z i n g corPibinakions of p a r e n t s no t h e r e t o f o r e combined, and some new selections, These c ros se s w i l l be inc luded i n t h e above progeny t e s t t o provide additional variation f o r r e c u r r e n t s e l e c t i o n .

A second progeny t e s t wi13 fo1Low which will i nc lude the remaining s e l e c t t r e e s not y e t producing s t r s b i l i , and those f o r which complete sets of c ros se s are not ye t f i n i s h e d .

LITEMTURE CITED

Barnhar t , Michael Re 1976* A new compact pollinator, USDA Fer*Serv, Res, Note RM-310, 2 p , , Rocky Mt, F o r , 2nd Range Exp, S t n , , F o r t Co l l i n s , Colorado.

Brown, Ian R, 1941. Flori~ering and seed produc t ion i n g r a f t e d c lones of Scots pine. S i l v a e Genet. 20(4) :12l-132,

Ebel, Bernard H., FZawe11, Thomas K . , Drake, Loyd E., Yates, Warry 0, 111, and D e Barr, Gary LO 1975. Southern p i n e seed and cone i n s e c t s . USDA For, Serv. Gen. Tech. Rep, SE-8, 40 p. Southeastern For' Exp, S tn* ,and Southeas te rn Area, S t a t e and P r i v a t e F o r , , Atlanta, G a ,

Fo r she l l , C h r i s t i n a Plyme 1974. Seed development after self-pollination and c ros s -po l l i na t i on of Scots p ine , Pinus sylvestris I,, Studia ForestaJia Suecica, Skogshogskolan, Royal C o l l D of F o r , , Stockhold $10, 118, 37 p e

~ e r h o l d , Henry D. 1968. Mini-bags for tree breeding. Silvae Genet. 15(1): 31-32,

Griffing, B. 1956. Concepts o f general and spec i f ic combining a b i l i t y in r e l a t i o n to d i a l l e l crossing systems, Austral, J, B i s i . S c i , 9 ( 4 ) : 4 6 3 - 493.

Johnson, H., C. 0. Kiel lander and E. Stefannson. 1953. Cone development and seed. q u a l i t y on pine grafts. Sv, Skogsv, ~Zren Tidsk r , %1:35&359.

Karrfalt , Robert . and B e D. CerhoLd. 1973. Inter-population mating8 i n Scotch p ine : flowering and seed y i e l d s . The Penn. St. Univ., Agr i c . Exp. Stn , R e s * Briefs 7(1):15-19,

Karrfalt, Robert P., 4. D. Gerhold and E. Ft. Palpan t . 1975. Inter-racial hybridization in Scotch p ine : geographic flowering pa t t e rns and cross- b y Silvae Genet, 24(4) :107-119,

Krugmn, Stanley %, and James L, Kenkinson. 1974, Pinus E. (Jn) Seeds o f Woody Plants in the United States. U.S. Dep. Agric., For . Serv., Phgric* Handbook 450, 883 p,

Read, R a b h A, 1971. Scots pine in eastern Nebraska: a provenance s tudy , USDA For. S e r , Res, Pap, E@4-78, 13 p; Rocky Kt, POP, and Rmge Exp. Stn. . Fort Col l in s , Golo*

Sehrm, @, Me, He DI Gerbald, Re Fa West and E , S. Hamlltan, 1975. Genetic variances of Scotch pihe: environment and age e f f e c t s , For, S c i , 21 (4) :330- 339 *

Skiiling, Darroll Be and Thomas B. NicholLs, 1974. Brown s p a t needle disease--bfology and con t ro l i n Scotch p i n e plantations. USDA For* Serve R e s , Pap. N C - I q 9 , 19 p, North Cent, For, Exp. S t n , , S t . Paul, Minn.

Van Haverbeke, David F a , WaPrer T, Bagley and Ellsworth H * Benssn. 1973. Breeding a better Christmas tree. Univ. Ne'br. Ccll. Agr ic . Farm, Ranch and Home Quarterly, 2 2 ( 3 ) : 2 - 4 .

Van Maverbeke, David F, 1974. A Scots pine clonal seed orchard of provenance origfn, Pro@e 9th Cent, States For, Tree Improve Conf,, h e s , Iowa, Oct. 9-11, 1974, p. 62-70.

Van Haverbeke, David F, (In press), Soaking and r e t u ~ l b l i n g controlled- pollinated Scots p ine cones increases seed y i e l d s $y one-third. Tree Planters "~otes

".

Wright, J , 5p;rl and W, Ira B u l l , 1963, Geographic var ia t ion in Scotch pine-- results of a 3-year Michigan study, Si4vae Genet. 12: 1--25*

Wright, J , W e , S, S , Pauley, R, 5, Polk , Jaimer 9, Jokela and R e A, Read, 1966. Perfamanse s f Scotch pine varieties in the North Central region. Silvae Genet, 15:10%-%101

Zeaser , Donald B . 1976. Inter-varietal hybr ids of Scotch pine: F1 characteristics. Unpubl. M.S. Thesis. The Penn. St. Univ., School of Forest Resourcess

Zobel, B e J . , R. J. Weir and J. B . Je t t . 1972. Breeding methods to produce progeny for advanced-generation selection and to eva lua t e trees* Can. J . For , Res, 2 ~ 3 3 9 - 3 4 5 ,