NEW ZEALAND JOURNAL OF BOTANY. Department of Scientific and Industrial Research, Wellington

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1 NEW ZEALAND JOURNAL OF BOTANY Department of Scientific and Industrial Research, Wellington Editorial Board.- Dr E. ]. Godley, Professor G. T. S. Baylis, Dr E. G. Bollard, Professor R. G. Thomas Editor: Prudence M. Hilson VOLUME 3 DECEMBER 1965 NUMBER 4 BREEDING SYSTEMS IN NEW ZEALAND GRASSES VI. CONTROL OF GYNODIOECISM IN CORTADERIA RICHARDII (ENDL.) ZOTOV H. E. CONNOR Botany Division, Department of Scientific and Industrial Reseaich, Christchurch (Received for publication 13 July 196}) SUMMARY Male sterility in gynodioecious C, richardii is controlled by a single recessive gene; three genotypes are recognised: MsMs 5, Msms S, and msms?. Progenies from crosses to females are superior in vigour to progenies from MsMs 5 and to those from selfed MsMs 5 and Msms 9. In ovule production females have an advantage over hermaphrodites, but this difference and a small difference in germination are insufficient to maintain an equilibrium state except at the lower female frequencies. INTRODUCTION Gynodioecism, the presence of hermaphrodite and female plants in populations and an outcrossing breeding system, while common in dicotyledonous genera was not observed as the breeding system in any of the grasses until it was recorded in indigenous Cortaderia richardii by Connor and Penny (I96). This system was later noted in C. fulvida and C. toetoe (both indigenous species) by Connor (1963), and more recently in C. selloana naturalised in New Zealand, and in two other South American species (Connor, 1965). N.Z. ]. But. 3 :

2 234 NEW ZEALAND JOURNAL OF BOTANY [DEC. Results from experiments conducted to determine the genetics of gynodioecism in long-lived decaploid Cortaderia richardii indicate control of male sterility by a single recessive gene. An examination of some of the components of fertility reveals that females are more fertile than hermaphrodites, but not to the extent estimated by Lewis (1941) to be necessary to maintain the range of female frequencies found in wild populations. MATERIALS AND METHODS Plants raised from seed collected in the wild from Ashburton Gorge, Canterbury, were used in these experiments. Ten hermaphrodite plants were selfed, and seed was set in all of them. Eight of these hermaphrodites were used as pollen parents on two female plants (one of them on to both females). Seed-set was good in these crossings except in 32 2 X 46 g, which yielded only nine seeds. Twenty plants of each family were grown in the Botany Division experimental garden at Lincoln for scoring sex forms. This sample size is sufficient to detect any segregation in selfed hermaphrodites or in crosses; it is not large enough, however, to give good segregation ratios, but because C. richardii plants take a minimum of four years to come to flower and because of their large size at first flowering, the desirable very large family could not be raised. Crosses and sellings were made in December I96, and some plants first came to flower in December 1963; all plants flowered in November- December Those plants that flowered in both years were rechecked for sex form; no reversal of sex has been observed. GENETIC BASIS OF MALE STERILITY Results presented in Table 1 indicate two hermaphrodite genotypes; on selfing, one segregates both females and hermophrodites and the other is non-segregating with all progenies hermaphrodite. Females crossed to segregating hermaphrodites give segregating progenies while females crossed to non-segregating hermaphrodites yield hermaphrodites only. Families raised from seed from three open-pollinated non-segregating hermaphrodites contained all hermaphrodites. No families from segregating hermaphrodites were present in the original open-pollinated lots selected, but these are now being raised. These results indicate that a single recessive gene controls male sterility, in which case the two hermaphrodite genotypes are MsMs and Mstns and the single female genotype is the homozygous recessive mstns. Families 3826 and 3827 from selfed Mstns 2 are not heterogeneous (^2 = 2-41) and the combined families would fit the ratio 3 5 : 1 $, x 2 = The three families from msms X Mstns g are not heterogeneous (x 2 2 = 1*24) and would fit the ratio 1 S : 1 $, x 2 = Jain (1959) concluded that in most species where male sterility was known to be inherited a single recessive factor was involved. Although Jain's list contained some grasses, in none of them is gynodioecism established as the

3 1965] CONNOR-BREEDING SYSTEMS 235 breeding system in wild populations as it is in Cortaderia. Preliminary results from studies on C. selloana indicate that a single gene controls male sterility. TABLE 1 Sex form in families from selfing, crossing, and open-pollination Plant No. Treatment Family No. 6 S Selfed 3)» Non-segregating 5, Ms Ms 34f X X X 6 34 X39 34 X 48 Crossed»> msms X MsMs yields Msms 5 only Open-pollinated» Non-segregating $,MsMs Selfed Segregating 9, Msms 32f X X X 26 Crossed msms X Msms Yields Msms S and msms ffemale parent listed first. ADVANTAGES TO FEMALE PLANTS Lewis (1941) indicated that when a single dominant or recessive gene controls male sterility females must be more than twice as fertile as the hermaphrodites, if females are to remain in the populations. Some of the factors measuring the relative fertility of hermaphrodites and females are discussed below. EFFECT OF INBREEDING ON HERMAPHRODITES Families from selfed hermaphrodites were clearly less vigorous than those from crosses to females (Table 2). Open-pollinated Ms Ms g produced families equally as weak as those from the selfing of both hermaphrodite genotypes, and as these progenies seem to be from intercrossing to both MsMs and Msms, these results suggest that there is a disadvantageous maternal effect due to the MsMs genotype.

4 TABLE 2 Measurements of four characters on plants grown in uniform environment at Lincoln Origin Genotypes Mean Wet Weight (lb)/plant Mean Culms Ht. (cm) Mean No. Panicles/Plant Mean Panicle Length (cm) z Crossing? X MsMs and? X Msms msms and Msms ± 6-5** (n= 1) ± 3-5** (n= 11) 14-5 ± 5-3** (n= 11) 61- ± 1-** (n = 49) N w > 2 Open-pollination of MsMs 5 MsMs 5 and Msms S 36-3 ± 4-7 (n = 6) ± 6-5* (n=31) 8- ± 6-9 (n = 59) 52-9 ± 2-4 (n=15) IB z > o Selfing of MsMs 5 MsMs 5 and Msms S and msms ± 4-5 (n= 1) ± 3- (n = 72) 93-3 ± 4-6 (n = 92) 3-4 ± 1-4 (n = 34) **Significantly different (P = -1) from open-pollinated and selfed families. *Significantly different (P = -5) from families from selfing. D n

5 1965] CONNOR - BREEDING SYSTEMS 237 REPRODUCTIVE CAPACITY Panicles per Plant The number of panicles per plant is given in Table 3; these are sorted from the data in Table 2. Hermaphrodites produced more flower heads than did females in the families from crossing, but the number of female plants in the sample was very small. Females in families from selling also yielded fewer panicles than did hermaphrodites, but the difference was not significant. Spikelet Number The number of spikelets at the fifth panicle node from the base (about mid panicle) was counted on 4 g and 25 9 randomly chosen plants (Table 3). More spikelets were present on females than on hermaphrodites in the families from crossing, but not in those from selfing. Florets per Spikelet The number of florets per spikelet was counted in 1 spikelets in each of 65 randomly chosen plants. There was no difference in the number of florets per spikelet between females and hermaphrodites in families from crossing, but females in families from selfing differed significantly from hermaphrodites (Table 3). Seed-set Percentage seed-set was determined by counting the number of caryopses set under open-pollination in 5 spikelets per plant in 53 randomly chosen plants (Table 3). No significant differences were detected and seed-set was high in all genotypes. Seed Length and Seed Weight The difference in gynoecium size between hermaphrodites and females (see illustration in Connor, 1963) is seen again in seed size. Caryopsis length and weight were measured in two seasons (Table 4). Seeds from females are longer than those from the two hermaphrodite genotypes, while seeds from females were significantly heavier in samples only. Female and hermaphrodite plants originating from crosses yield longer seeds than do plants derived from selfing of hermaphrodites. Germination Some difficulties were encountered in the germination of seed from the original selfings and crosses and important data could not be adequately gathered. Since then, by using bottom heat, a quick germination of seed has been possible. Tests were conducted in 1965 on seed from plants of the three genotypes; details of origins and results are in Table 5. One hundred seeds were sown in each test. Germination of open-pollinated seed from msms $ and Msms g was significantly different (P = -5). Seed from selfed MsMs g and Msms 5

6 TABLE 3 Flower and seed production Origin Genotype Mean No. Panicles/Plant Mean No. Spikelets at 5th Node Mean No. Florets/Spikelet Mean Percentage Seed-set 2! Crossing Msms 5 msms 9 N ± 5-6 (n = 99) (n = 25) 2-31 ± -6 (n = 21) 9-3 ± 2-3 (n = 12) ^ 17-8 ± 15-* (n = 11) 357 ± 21** (n = 15) 2-23 ± -5 (n = 15) 87-1 ±3-82 (n = 15) Z Selfing M i x e d M J A T T $ ± 4-9 (n = 8 ) 265 ± 25 (n = 1 5) ± -1 (n = 13) ± 5-8(n = 1 ) and Msms 5 msms ±13-4 (n = 12) 254 ± 3 (n = 1) 1-76 ± -9*(n = 1) 94-7 ± 1-1 (n = 1) Open-pollination of MsMs 5 Mixed Ms Ms S and Msms 5 8- ± 6-9 (n= 59) 2-38 ± -15 (n = 6) 95-8± -9 (n = 6) fa a: r o Panicles/plant Spikelets at 5th node: Florets/spikelets: within crossing families, *significantly different (P = -5) from S. within crossing families, **significantly ditterent different ^ (P = 1} -1) from r within selfed families, significantly different (P = -5) from S and also from crosses and openpollination open-pollination (P = 1) -1). D SI o

7 TABLE 4 Seed size (upper line, length mm; lower line, weight caryopses mg) From seed collected in wild 2-78 ± -8 (n = 8) 18 ± 16 (n = 8) 2-6 ± -12 (n = 5) 15 ± 25 (n =4) 3-21 ± -1** (n = 8) 126 ± 13 (n = 8) 9 zz o fa Crossing Selfing 2-42 ± -6 (n = 6) 131 ± 14 (n = 6) 2-59 ± -4 (n= 16) 143 ± 4 (n= 16) 2-95 ± -4** (n= 12) 169 ± 6 (n=12) 2-57 ± -4* (n = 1) 157 ± 6 (n = 1) ta ta O Z a Caryopsis length **Significantly different (P = -1) from hermaphrodites Crossing origin: **significantly different (P = -1) from Msms, and also from msms. Selfing origin: *significantly different (P = -5) from MsMs. r/i to

8 24 NEW ZEALAND JOURNAL OF BOTANY [DEC. had significantly lower germination than that from open-pollination, while germination of open-pollinated seed from S t msms 9 and MsMs Q plants did not differ significantly from seed from Msms g plants derived from crossing. TABLE 5 Percentage germination. Means and -95 confidence intervals are retransformed values. Origin of Seed Parent Treatment Genotype of Seed Parent Msms MsMs Crossing Openpollinated Selfed 86 7; (n = 15) 9 (n= 19) 59-; (n = 8) Selfing Opeiipollinated Selfed 73 ; (n = 1) ; (n = 9) 45-8; (n = 4) Within msms and Msms difference significant (P = -1), and within MsMs difference significant (P = -5). ^Significantly different (P = -5) from open-pollinated msms derived from crossing. DISCUSSION The most adequately documented post-darwinian case of females being at least twice as fertile as hermaphrodites (fertile in the sense of setting seed) is described in Burrows (I96). Formal names replacing the vernacular names used in I96 are in Burrows (1962). In Pimelea oreophila and P. serkeo-viilosa, fruit setting on females was times greater than on hermaphrodites, in P. prostrata 1 times, and in P. traversii twice as much. Lewis and Crowe (1956) recorded in Origanum vulgare 75% seed-set in hermaphrodites and 89% in females; this difference was highly significant. McCusker (1963) found in Leucopogon meldeucoides that females set more fruits than did hermaphrodites, though seed-set in fruits from the two sex forms did not differ 1. Of the various factors examined which could contribute to a selective advantage to females in populations of C. richardii, only in the number of spikelets per panicle, as estimated from mid-panicle counts, are females in any way superior to hermaphrodites. This value is estimated at l - 34 times better than that from the most vigorous hermaphrodites, i.e., those produced from crosses to females. But this value on its own, assuming equal panicle production, is lower than the minimum of two suggested by Lewis. Germination results do not suggest a rigorous mechanism favouring the

9 1965] CONNOR - BREEDING SYSTEMS 241 maintenance of females in natural populations, but they show clearly that selfed seed is at a disadvantage. The evidence adduced earlier (Tables 2 and 3) showed that families from cross-pollinated MsMs g were much less vigorous than crosses to females. This lack of vigour is tentatively identified as a maternal effect from the MsMs genotype and one which would lead to severe losses within its progeny in competition with plants derived from crosses to females. As yet, no comparison between progenies from crosses to females and openpollinated Msms g has been made, so it is impossible to indicate whether or not these show some similar trend. An advantage to the progeny from females over the progeny from homozygous dominant hermaphrodites is clear, and estimating from panicle production and length and the number of spikelets at the fifth panicle node, this advantage to females is about 2*7. MAINTENANCE OF FEMALES IN POPULATIONS The frequency of females in wild populations of C. richardii was reported in Connor (1963) and the values lay between 24 and 53% with a mean of 37*6%. No estimate of the frequencies of the two hermaphrodite genotypes is available, as there is no way of distinguishing between them in the field. Certainly more than one generation of these long-lived, slow-maturing plants was present in the stands examined and it is not possible to indicate what, if any, of the actuai values obtained might be an equilibrium value for frequency of females in the wild. The Mackenzie Pass population, where all plants were hermaphrodites, may be explained on the assumption that the original migrants into the site were MsMs. There is no evidence that the mutation Ms > ms has occurred there, but if it has, it has had no apparent effect on population structure. For most of the C. richardii populations where the frequency of females was determined, the calculations given in Lewis (1941) would indicate that the females must be at least four to six times as fertile as the hermaphrodites for an equilibrium to be maintained. The evidence so far available would suggest that female fertility (seed germination included) is about three times that of MsMs q and about one and one-half times that of Msms g. Values such as these do assist in maintaining females in the next generation at a higher frequency than if all genotypes were equal in flower production and germination. The factors controlling the frequency of females in natural populations should emerge from recent experiments that will take a further four years to reach completion. Data from these should illuminate such questions as selective pollination, imbalance in segregation ratios, and possible maternal effects on progenies from Msms genotype. These additional data should permit the construction of a model accounting for natural populations. A preliminary analysis shows that with flower production and germination respectively at msms 9 2-7, 1-14; Msms g 2-, 1-; MsMs Q 1-, 1-; and without selection, estimated equilibrium values would be reached for populations containing about 3% females; for example, in the Scamander Stream sample in Connor (1963).

10 242 NEW ZEALAND JOURNAL OF BOTANY [DEC. ACKNOWLEDGMENTS I am grateful to Mr A. H. MacRae, Botany Division, for much technical help and to Miss E. Stevenson, Applied Mathematics Laboratory, D.S.I.R., Lincoln, for all computations. REFERENCES BURROWS, C. J. 196: Studies in Pimelea. I. The Breeding System. Trans, roy. Soc. N.Z. 88: : II. Taxonomy of Some Mountain Species. Trans, roy. Soc. N.Z. Botany 1: CONNOR, H. E.; PENNY, E. D. I96: Breeding Systems in New Zealand Grasses. II. Gynodioecy in Arundo richardii Endl. N.Z. ]. agric. Res. 3: CONNOR, H. E. 1963: IV. Gynodioecism in Cortaderia. N.Z. ]. Bot. 1: : V. Introduced Species of Cortaderia. Ibid. 3: JAIN, S. K. 1959: Male Sterility in Flowering Plants. Bib. Genet. 18: LEWIS, D. 1941: Male Sterility in Natural Populations of Hermaphrodite Plants. New Phytol. 4: LEWIS, D.; CROWE, L. K. 1956: The Genetics and Evolution of Gynodioecy. Evolution 1: MCCUSKER, A. 1963: Gynodioecism in Leucopogon melaleucoides A. Cunn. Proc. Linn. Soc. N.S.W. 58: