Thesis (MScAgric)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The objective of this study was to obtain more information regarding the characterisation of Afrikaner (A), Hereford (H) and Simmentaler (S) breeds in an initial crossbreeding programme and subsequent composite development. This involves the estimation of breed additive effects, breed maternal, individual heterotic effects and maternal heterotic effects in the initial crossbreeding phase and the estimation of genetic parameters and prediction of breeding values in later generations for birth weight (BW), weaning weight (WW) and cow efficiency (CE; WW/dam weight" 75 x 100) in an intensive environment under high stocking rates. In the analysis of the initial crossbreeding phase, the S breed direct effects, expressed as deviation from the general mean, were positive (P :s; 0.01) for both BW and WW. Hereford and A breed direct effects were negative (P :s; 0.01) for both BW and WW. Afrikaner direct maternal effects were positive (P :s; 0.01) for both BW and WW. The H direct maternal effect was negative (P :s; 0.05) (- 2.8%) for WW. Simmentaler maternal effect was negative (P :s; 0.01) for BW but non-significant (P ;:::0:.05) for WW. Individual heterotic effects for BW were significant (P:S; 0.01) in H x S (3.5%) and S x A (11.0%) only. Individual heterotic effects were positive (P :s; 0.01) for WW, with that of the H x A (9.8%) and S x A (6.7%) crosses exceeding the H x S (3.1%) cross. Maternal heterotic effects were non-significant (P ;:::0:.05) for both BW and WW. Investigations of the contributions of the A, Hand S during composite development in later generations, respectively, were made to estimate direct heritabilities (h2 a) and maternal heritabilities (h2 m) for BW and WW of the calf and CE of the dam. Calves were born between 1968 and 1993 (n = 52628). Calves of this composite population had varying levels of A, Hand S genes ranging from o to 75%, 0 to 100% and 0 to 96.9%, with an average of 4.3,19.3 and 33.4%, respectively. For the A, direct heritabilities fitting unitrait models were 0.67, 0.53 and 0.19 for BW, WW and CE, respectively, with corresponding estimates of h2mbeing 0.22, 0.36 and 0.58. Genetic correlations between direct and maternal effects (ram)were negative for all three traits, varying from -0.32 to - 0.62. Direct breeding values for BW increased and reached a maximum value at 0.11 proportion of A. The maternal breeding values for BW decreased linearly between 1.6 to 37.5% A proportion and increased linearly between 37.5 to 75% A proportion. For WW, the direct breeding values decreased linearly with increasing A proportion, while the maternal breeding values were not affected by proportion of A. Cow efficiency was unaffected by an increase in proportion of A. For the H, direct heritabilities fitting unitrait models were 0.67,0.52 and 0.21 for BW, WW and CE, respectively, with corresponding estimates of h2mbeing 0.22, 0.36 and 0.60. Genetic correlations between direct and maternal effects (ram)were negative for all three traits, varying from -0.32 to - 0.64. Direct breeding values and maternal breeding values for BW and WW decreased with increasing proportion of H. Direct breeding value for CE increased, while the maternal breeding value for CE reached minimum value at 0.62 proportion ofH. For the S, direct heritabilities fitting unitrait models were 0.66, 0.53 and 0.21 for BW, WW and CE, respectively, with corresponding estimates of h2m being 0.22, 0.36 and 0.59. Genetic correlations between direct and maternal effects (ram)were negative for all three traits, varying from -0.32 to - 0.63. Direct breeding values for BW and WW decreased and maternal breeding values increased with increasing proportion of S. Cow efficiency was unaffected by an increase in proportion of S. The study suggests that in the initial crossbreeding phase, purebred S breeding seems to be the best breeding practice for this environment and that during composite development, high A and H contributions could lead to low BW and WW (except the maternal contribution of the A for BW and WW). The advantage of the S lies more in the maternal contribution than in the direct contribution suggesting that the S is a large-framed maternal line rather than a terminal sire line. / AFRIKAANSE OPSOMMING: 'N WAARDEBEP ALING VAN DIE BYDRAE VAN DIE AFRIKANER, SIMMENTALER EN HEREFORD TYDENS KOMPOSIETE RASONTWIKKELING BY VLEISBEESTE: Die doel van die studie was om inligting aangaande die karakterisering van die Afrikaner (A), Hereford (H) en Simmentaler (S) rasse tydens die oorspronklike aanvangsfase van kruisteling en daaropvolgende komposiet ontwikkeling te verkry. Dit het die beraming van direkte additiewe, individuele heterose, direkte materne en materne heterotiese effekte tydens die aanvangsfase van die kruisteeltprogram, die beraming van genetiese parameters en die voorspelling van die teeltwaardes in latere generasies behels. Die eienskappe wat ingesluit is, is geboortegewig (BW), speengewig (WW) en koeidoeltreffendheid (CE; WW/koeigewigo.75 ). Hierdie kudde is in 'n intensiewe maar onder 'n hoë weidingsdruk omgewing aangehou. Tydens die ontleding van die eerste kruisteeltfase is die direkte additiewe effekte vir die S, uitgedruk as afwyking van die algemene gemiddelde, vir beide BW en WW positief (P ~ 0.01). Direkte additiewe effekte vir die H en A was vir beide BW en WW negatief (P ~ 0.01). Afrikaner materne effekte was vir beide BW en WW (P ~ 0.01) positief. Die H direkte materne effekte was negatief (-2.8%) (P ~ 0.05) vir WW. Simmentaler maternal effekte was ook vir BW negatief (P ~ 0.01), maar nie-betekenisvol (P 20.05) vir WW. Individuele heterose was slegs betekenisvol (P ~ 0.01) vir kombinasies van H x S (3.5%) en S x H (11.0%) vir BW. Individuele heterose was positief (P ~ 0.01) vir WW waar H x A (9.8%) en S x A (6.7%) kruisings dié van die H x S (3.1%) kruising oortrefhet. Materne heterose was vir beide BW en WW nie-betekenisvol (P 2 0.05). Die relatiewe bydraes van die A, H en S is ook tydens komposiet-ontwikkeling bereken. Direkte additiewe oorerflikhede (h2 a) en materne oorerflikhede (h2m) is vir BW en WW van die kalf en CE van die koei beraam. Kalwers in die komposiet kudde, gebore tussen 1968 en 1993 (n = 52628), het variërende vlakke van A, H en S gene. Die samestelling het gevarieer van 0 - 75%, 0 - 100% en 0 - 96.9%, met 'n gemiddeld van 4.3, 19.3 en 33.4%. Vir die A was die direkte erfbaarhede (h2 a), soos deur die passing van 'n enkeleienskapmodel beraam, 0.67, 0.53 en 0.19 vir onderskeidelik BW, WW en CE, met ooreenstemmende beramings van 0.22, 0.36 en 0.58 vir h2 rn- Genetiese korrelasies tussen direkte en mateme effekte (ram)was almal negatief en het tussen -0.32 en -0.62 gewissel. Direkte teelwaardes vir BW het met toenemende A-bydrae gestyg en het 'n maksimum waarde by 0.11 bereik. Die mateme teelwaardes vir BW het lineêr gedaal tussen 1.6 en 37.5% A-bydrae en het weer lineêr tussen 37.5 en 75% Abydrae gestyg. Vir WW het die direkte teelwaardes lineêr met toenemende A-bydrae gestyg, terwyl die mateme teelwaardes nie deur A-bydrae beïnvloed was nie. Koeidoeltreffendheid was nie deur 'n toename in A-bydrae beïnvloed nie. Vir die H was die direkte erfbaarhede (h2 a), soos deur die passing van 'n enkeleienskapmodel beraam 0.67, 0.52 en 0.21 vir onderskeidelik BW, WW en CE, met ooreenstemmende beramings van 0.22, 0.36 en 0.60 vir h2 rn- Genetiese korrelasies tussen direkte en mateme effekte (ram)was almal negatief en het tussen -0.32 en -0.64 gewissel. Direkte teelwaardes en mateme teelwaardes vir BW en WW het met toenemende H-bydrae gedaal. Direkte teelwaarde vir CE het ook met toenemende If-bydrae gedaal, terwyl die mateme teelwaarde 'n minimum waarde by 0.62 H-bydrae bereik het. Vir die S was die direkte erfbaarhede (h2a), soos deur die passing van 'n enkeleienskapmodel beraam 0.66, 0.53 en 0.21 vir onderskeidelik BW, WW en CE, met ooreenstemmende beramings van 0.22, 0.36 en 0.59 vir h2 m- Genetiese korrelasies tussen direkte en mateme effekte (ram)was almal negatief en het tussen -0.32 en -0.63 gewissel. Direkte teelwaardes vir BW en WW het gedaal, terwyl die mateme teelwaardes met toenemende S-bydrae gestyg het. Koeidoeltreffendheid was nie deur 'n toename in S-bydrae beïnvloed nie. Die bevinding was dat tydens die ontleding van die eerste kruisteeltfase die teling van suiwer S aanbeveel word en dat tydens komposiete-ontwikkeling toenemende A- en H-bydraes neig om aanleiding te gee tot afnames in BW en WW (behalwe die mateme bydrae van die A vir BW en WW). Die S-bydrae se voordeel is meer in die mateme bydrae as in die direkte bydrae geleë en dui dus aan dat die S as 'n mateme grootraam lyn i.p.v. as 'n terminale bullyn gebruik moet word.

The mushroom, Agaricus bisporus (Lange) Imbach, has been in cultivation since 1650 and is now a major protected crop with a value world-wide in excess of £2,OOOm. Despite its importance as a crop species and long history of cultivation, little work has been done on genetics and strain improvement. The mushroom is 2-spored and single-spore cultures are usually fertile. Studies of the breeding system of the mushroom are described based on the behaviour of cultures derived from aberrant 3- and 4-spored basidia. It is shown to be a secondarily homothallic species with a single mating-type factor. Methionine and proline auxotrophs are identified and two morphological markers are characterised, the first resulting in the constitutive production of fruit-body initials in culture and the second in altered gill morphology. Studies of 4-spored wild Agaricus species are described. A. bitorguis, ~ macrosporus and A. nivescens are shown to be unifactorially heterothallic. Nuclear numbers in homokaryons and heterokaryons of these species are determined and compared with A. bisporus. A scheme is proposed for the evolution of the secondary homothallism seen in ~ bisporus from a 4-spored heterothallic ancestor. Approaches to mushroom strain improvement are considered in detail and a breeding strategy based on the use of induced fungicide resistance is described. Following this strategy mutants resistant to the fungicides carboxin, benodanil and tridemorph have been obtained and evaluated in vitro and in vivo. Four of these mutants are the subject of a patent under the aegis of the British Technology Group. Finally, the mechanism regulating secondary homothallism has been studied. A predictive hypothesis, the random migration of nuclei in pairs from the basidium into the spores, has been tested in the model 2-spored organism Coprinus bilanatus nom. provo

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This investigation examined the efficiency of various screening procedures which could be used in breeding for increased production of root-proliferating (RP) genotypes of alfalfa (Medicago sativa L. s. l.). Also investigated were relationships between RP and winter growth characteristics in populations derived from crosses between dormant, RP clones and nondormant, non-RP clones. In addition, this investigation also considered the inheritance of the RP habit. Plants from an 11-month F₁ progeny test containing 3508 offspring were qualitatively analyzed for RP expression using three pairs of screening procedures. Procedures compared included: (1) direct-seeding vs. transplanting; (2) use of characterized parental clones (known RP-expressing genotypes selected from field nursery) vs. uncharacterized parental clones (genotypes derived from RP seed lots with no prior knowledge of their ability to express the RP habit) in RP x nondormant crosses; and (3) low vs. high harvest frequencies. A low frequency (3.3%) of F₁ plants exhibited adventitious shoot formation. No differences were observed in the frequency of RP-expressing genotypes between the direct-seeded and transplanted treatments or between the low and high harvest frequency treatments. Characterized RP parents produced a hybrid population with a significantly higher frequency of RP-expressing genotypes than did the F₁ population derived from uncharacterized RP parents. Average winter forage production of the F₁ hybrids were similar in magnitude to the midparent value. Plant height was significantly and positively correlated with forage yield and could be used as an accurate indicator of winter forage yield in analyses of RP segregants. Estimates of components of genetic variance for RP expressivity indicated a predominance of additive effects and narrow sense heritability of 8.4%. Family selection and progeny testing are suggested for maximum breeding progress.

Curly mesquite (Hilaria belangeri (Steud.) Nash) is a palatable, nutritious range grass in the southwestern United states. A research project was initiated in 1988 on plant material collected within Arizona to determine the value of this species as a turfgrass, if sufficient genetic variation existed in vegetative , reproductive, and germination traits to allow for improvement of the turfgrass value by breeding, and if this species could be successfully established by seeding. curly mesquite can withstand the rigors of turfgrass cultural practices (mowing and fertilizing), while maintaining an attractive, healthy appearance. Plant material from five separate geographic origins was subjected to 5 cm and 10 cm heights of cut, and a no cut treatment, along with nitrogen applications of 0, 48, and 96 kg ha⁻¹ yr⁻¹ in a randomized complete block split-split plot design. cutting at 10 cm, and application of 96 kg N ha⁻¹ yr⁻¹ produced the best color and highest ground cover. Control (uncut) plots exhibited low vigor and color. Broad-sense (h²(b)) and narrow-sense (h²(n)) heritability estimates were computed for measured and rated characters on clones and their open-pollination progeny grown at Safford (S) and Tucson (T), AZ. Estimates of h²(b) of measured characters were: leaf length 0.29 (S) and 0.45 (T), stature 0.83 (S) and 0.71 (T), and flowers•spike⁻¹ 0.40 (S) and 0.36 (T). Significant variation was not observed in leaf width. Significant h2 n estimates of 0.31, 0.51, and 0.30 were obtained for leaf length, stature, and flowers•spike⁻¹ , respectively. Broad-sense heritability estimates ranged from 0.46 to 0.79 for color, and 0.47 to 0.69 for density ratings. Cumulative germination percentages had h2 b estimates ranging from 0.45 to 0.61. Hard seed (%) and seed weight (mg 100 seed-l) had h²(b). estimates of 0.83 and 0.95, respectively. Successful seedling establishment occurred after June, July and August sowings. Ground cover at the close of the season was greatest for the June seeding. A significant difference did not exist between the ground cover means of seeding rates (1 and 2 gm m⁻²). The results of these investigations clearly warrant further efforts in the development of curly mesquite into a low maintenance turfgrass.

The cytological and breeding behavior of barley with 8 pairs of chromosomes, of which 2 pairs are interdependent were evaluated. The 8II material originated from selfed progeny of a Balanced Tertiary Trisomic 57a msg16. Chromosome interdependence was established after a naturally occurring reciprocal translocation between the normal chromosome 5 and the extra interchanged 57a chromosome. The interdependent chromosomes are fragment chromosomes. A Male Sterile Facilitated Recurrent Selection Population (MSFRSP) of 8II plants was developed. Eight chromosome paired plants were crossed onto male sterile plants from barley Composite Cross XXXII. The F₁ plants from the 7II x 8II crosses carried a characteristic 15-chromosome cytotype. In the F₂ of this cross, 5 different cytotype classes of progeny were isolated by root-tip chromosome and microsporocyte analyses: 7II, F₁, 8II, tertiary trisomic where the extra chromosome is a fragment chromosome and a Unique-16 chromosome cytotype which consisted of 6 normal pairs, one pair of fragments, one normal chromosome 5 and one fragment chromosome from the other pair of fragments. The F₂ population was approximately 30% 7II, 50% F₁ and 20% 8II cytotype progeny. Microsporocytes observed from F₂ cytotype plants indicated that the 7II and 8II progeny went through normal meiosis. The F₁ cytotypes produced functional gametes with 7 normal chromosomes, 8 chromosomes equivalent to gametes produced by 8II plants and gametes with 7 normal chromosomes plus a fragment chromosome. The tertiary trisomic progeny produced functional gametes with 7 normal chromosomes and gametes with 7 normal chromosomes plus a fragment chromosome. The Unique-16 cytotype produced functional gametes with 7 normal chromosomes, 8 chromosomes equivalent to gametes produced by 8II plants, 7 chromosomes plus a fragment chromosome and 9-chromosome gametes with 6 normal chromosomes plus 3 fragment chromosomes, two of which are a pair. Crosses and their reciprocals between 7II plants and plants of each F₂ cytotype indicated that the cytological stabilty of an 8II or 7II population would be disrupted if contaminated by pollen from 7II or 8II plants respectively. Growing the populations in physical isolation from each other is a must in order to maintain the cytotype of the population homozygous

Regrowth and yield of 23 Middle Eastern (ME) cultivars and the elite cultivar Lew were evaluated for twelve regrowth harvests in pure stands and 50:50 mixtures with Lew in 1988 at Tucson, Arizona. Stem elongation rate and crown shoot development were measured on selected ME cultivars and Lew in the spring of 1988. No significant differences in yield were observed between mixtures and monocultures. Few significant differences were observed over all yields among ME cultivars and Lew. Cultivars from Saudi Arabia and Egypt produced more forage than Lew in spring harvests. These cultivars developed crown shoots precociously and had high stem elongation rates during the first week of regrowth. Most ME cultivars had higher leaf area and leaf:stem ratio than did Lew. These findings suggest that ME cultivars may be useful in improving forage yield during the winter and spring and forage quality in elite nondormant cultivars.