4x-2x杂交创制马铃薯新种质

以二倍体马铃薯‘USW4’和Solanum chacoense杂交产生的F1株系‘XD-3’为材料,检测其2n花粉产率和花粉活力。研究结果表明,‘XD-3’能产生2n花粉,2n花粉产率约7.7%,且花粉活力较高,达74.75%。在此基础上,开展了4x-2x杂交,进行了4个不同的杂交组合,平均杂交结实率为36.5%,但平均种子数/浆果仅0.67粒。4个不同的杂交组合共获得19个杂交后代,2对父本特异的SSR引物检测结果表明,有14个株系可以确认为真杂种;杂种植株的倍性检测结果表明,7个为三倍体,7个为四倍体。大量三倍体的产生为n花粉的直接利用提供了一条新思路。     

4x-4x和4x-2x杂种后代高世代选系比重的比较

马铃薯的比重是加工企业要考虑的一个重要性状。本研究的目的是比较4x-4x和4x-2x杂种后代高世代选系的比重,试图利用单向有性多倍化(Unilateral sexual polyploidization,USP)的方法从二倍体栽培种向四倍体普通栽培种转育高比重基因。四倍体亲本为品种或高世代选系,二倍体亲本是普通马铃薯栽培种(Solanum tuberosum)双单倍体与二倍体栽培种富利亚(S.phureja)杂种的互交后代,或经轮回选择适应长日照的S.phureja-S.stenotomum杂种后代。从4x-4x和4x-2x组合各选出17个高世代无性系,以‘克新18号’(鲜食)和‘夏坡地’(薯条加工)为对照,采用随机区组设计,2011～2012年在黑龙江省的加格达奇评价了4x-4x和4x-2x高世代选系比重的表现。4x-2x和4x-4x后代高世代选系比重平均为1.0727和1.0659,二者差异极显著。但是,4x-2x内和4x-4x内无性系的差异仍达极显著水平。4x-2x四倍体后代HJ04-18-17,HJ04-27-41,HJ04-22-19以及HJ04-15-36比重高于对照品种‘夏坡地’,并和其有显著差异。结果表明,和4x-4x组合相比,4x-2x组合后代含有较高的比重。     

马铃薯新型栽培种(Neo-tuberosum)双单倍体杂种的研究

利用马铃薯新型栽培种(Neo—tuberosum,2n=4x=48)的双单倍体(2n=2x=24)与S.phureja (2n=2x=24)杂交,克服新型栽培种双单倍体雄性败育获得了成功。鉴定结果表明,杂种实生苗绝大多数保持了二倍性(2n=2x=24);实生苗可育株占总数78.36％。经减数分裂观察,入选的17个DP优良单株系主要是SDR型2n配子。为了选育出FDR型2n配子突变系,加强DP优系中的新型栽培种的遗传成分,即以D_(2012)—22(SY—m型)为母本,以DP优系为父本配制了回交组合,得到1000多粒种子,供进一步研究利用。     

棉花雌雄不育株小孢子发育的细胞学研究

棉花自然单倍体植株发现较早,并已通过孤雌生殖、双胚、种间杂交、半配生殖和辐射处理等获得了棉花单倍体。但棉花的花药培养尚未得到单倍体植株。棉花是二倍体和异源四倍体,染色体数为2n=2x=26和2n=4x=52,自然单倍体的概率很低。产生双胚的频率约为1/2～2.5     

在研究马铃薯对病原菌抗病能级育种工作中利用双单体和未减数配子的评价

在马铃薯抗晚疫病(Phytophora infestans)和抗乳状马铃薯胞囊线虫病(Globodera pollida)育种程序中,从双单体(2n=24)为亲本的杂交后代中获得的四倍体(4x)植株,大体上雌蕊是四倍体。在温室和田间对第一年和第二年块茎的测定表明,大多数高抗疫病的双单倍体的后代也表现高抗马铃薯晚疫病。用双单体PDH182和PDH247分别与一个四倍体杂交,选择一般配合力高且高抗马铃薯胞囊线虫病(PCN)的个体,其后代高抗晚疫病,且有1/3的植株也高抗PCN。对双单倍体×4x的杂交组合后代,在实生苗世代进行离体片鉴定,来快速筛选疫病抗性。观察来自不同抗疲病双单倍体后代的平均抗性,发现四倍体亲本之间是有差异的。试验同时证明,不同的双单倍体在疫病的抗性程度上,对后代的遗传传递力是有差异的。这可归因于未减数配子组成方式的差异,即减数分裂时第一次分裂的重组或第二次分裂的重组(SDR)都有差异。如果所有未减数配子都由SDR产生,则这种差异可归因于不同双单倍体之间抗疫病基因纯合程度上的差异。这种双单体×4x的杂交组合,每个授粉株只产生很少的后代。这少量的实生苗可能以比较高的频率产生带有目标性状的后代。由于必须种植这少量的实生苗,以便找到所要求的重组性状,所以在种植中寻求补救措施,而抗性鉴定要比常规育种方便得多。所得到的这些四倍体杂种可以同时在三个方面用于第二轮的育种工作:即,与其它的四倍体杂交;与双单倍体杂交以选择互补性状,以及产生综合多种抗性的双单倍体。     

双单倍体马铃薯染色体加倍的方法

本试验研究了马铃薯双单倍体(双单倍体是由四倍体栽培种花药培养产生的)植株加倍的两种方法。第一种方法:在MS培养基内附加NAA 0.1mg/1,而后加入秋水仙素0.2mg/l,用马铃薯双单倍体植株切断接种。经过40天培养,获得了加倍的四倍体植株,加倍频率为63.6%。第二种方法:将马铃薯双单倍体植株的茎,接种在含有2.4-D 1mg/l,萘乙酸0.025mg/l,KT 2mg/l的MS培养基上,在产生愈伤组织后诱导出再生四倍体植株,加倍频率为22.3%。     

快速测定活体马铃薯花柱上2X和X花粉间的竞争

由栽培马铃薯(4x)(S.tuberosum)与富利亚薯(2x)(S.phureja)杂交获得马铃薯双单倍体。依所采用的花粉不同,这些杂交所产生的后代包括不同数目的母体双单倍体、三倍体和四倍体杂种。由于存在胚株致死现象,仅有少量三倍体产生。由2x 花粉衍生得四倍体杂种,其频率比在以不同花粉授粉的条件下,从2x 花粉获得的期望频率要高些。H(?)glund(1970)提出两个假说来解释出现大量四倍体的问题,或是2x     

用组培法培养马铃薯—倍体和双单倍体进行染色体加倍的研究

分别取来自普通栽培种(S.tuberosum)的两个一倍体品系和两个双单倍体品系的茎段和叶片,用两步法进行组织培养来加倍其体细胞染色体数目。在以MS+2.25mg/1 BAP+5mg/1 NAA 为第一步的培养基上,从一倍体和双单倍体的茎段和叶片中获得了许多再生植株,其中约60%的加倍成植株(2n=2x=24或2n=4x=48),此结果表明此法是把单单倍体(以下简称一倍体)和双单倍体转化为纯合同源四倍体的有效方法。     

抗有丝分裂剂对产生小麦双单倍体的效果

研究了3种抗有丝分裂剂(秋水仙碱、氟乐灵和黄草消)在2个处理时间(48h和72h)及2种处理浓度〔秋水仙碱0.0125%(313μM)和0.025%(625μM),氟乐灵和黄草消均为5μM和10μM〕下对2个小麦(Triticum aestivum)品种(Pavon和Kitt)花药愈伤组织产生加倍单倍体植株的诱导效果。试验结果,秋水仙碱是最有效的染色体加倍剂,用秋水仙碱处理后,Pavon品种产生的再生植株中89%是双单倍体(2n=6x=42)。但是,用2种浓度的秋水仙碱处理72h后均产生了不利的影响。3种抗有丝分裂剂的不同处理浓度之间均无显著差异。对照处理(不加抗有丝分裂剂)的所有再生植株均为多倍单倍体(2n=3x=21)。上述结果表明,秋水仙碱仍然是最有效的染色体加倍剂,用秋水仙碱处理花药愈伤组织是通过花药培养获得高频率双单倍体植株的有效方法。     

中国马铃薯单倍体诱导进展

马铃薯产量、品质、加工等方面都较其他作物有更大的提升空间,但由于四倍体马铃薯存在遗传基础狭窄且复杂、难以创新等诸多问题阻碍了相关研究的深入开展。利用马铃薯单倍体或双单倍体植株有望解决上述诸多难题。马铃薯单倍体具有加速育种过程、提高选择效率等优点。马铃薯单倍体的获得包括花药培养、花粉培养、孤雌生殖、子房培养。其中,花药培养因更易取材,并且得到胚性细胞团、愈伤组织或胚状体的几率更大等优点而研究最为广泛。获得单倍体植株的成功率与试验材料的基因型、培养条件、培养基添加物等诸多因素相关。根据不同的诱导方法简要阐述了中国马铃薯单倍体研究的历史及进展。     

马铃薯4x×2x杂种无性一代产量及产量性状的表现

产生２ｎ花粉的Ｎｅｏ－ｔｕｂｅｒｏｓｕｍ双单倍体×Ｓｏｌａｎｕｍｐｈｕｒｅｊａ的二倍体杂种以及其与Ｎｅｏ－ｔｕｂｅｒｏｓｕｍ双单倍体的回交后代与普通马铃薯（Ｓ．ｔｕｂｅｒｏｓｕｍｓｓｐ．ｔｕｂｅｒｏ ｓｕｍ品种东农３０３进行了杂交。４ｘ杂种在株高方面表现出了很强的杂种优势。商品薯产量与４ｘ亲本无显著差异，但两个杂种群体的最高值分别超４ｘ亲本的２６０ｇ／株和６０ｇ／株。总产量杂种优势明显，但杂种单株结薯数多，平均块茎重小，这些是限制４ｘ×２ｘ杂种利用的不利因素，需要进一步地改善。     

Male sterility and 2n pollen in 4x progenies derived from 4x×2x and 4x×4x crosses in potatoes

Summary The objectives of these experiments were to evaluate male sterility (MS) and 2n pollen frequency in 77 4x×2x families and 26 4x×4x families. The 2x parents were haploid-species hybrids and the 4x parents mainly clones withS. tuberosum ssp.tuberosum (tbr) andS. tuberosum ssp.andigena (adg) in their genetic background. The female parents had different cytoplasms: adg, tbr,S. demissum (dms), andS. stoloniferum (sto). Families from female parents with adg or dms cytoplasm did not have MS plants. However, families derived from crosses of many tbr females with 2x hybrids and a 4x adg clone had a high percentage of MS plants; all the progenies from cv. Serrana (sto cytoplasm) possessed tetrad sterility. These results can be explained as due to an interaction between a dominant male sterility (Ms) gene with tbr and sto cytoplasms. Some MS 4x hybrids (tbr×adg) used as females had the Ms gene, but male fertility was restored in some plants of their progenies when they were crossed with 4x tbr clones. This indicates that some tbr clones have a fertility restorer gene (Rt). The results from both 4x×2x and 4x×4x families fit the expected ratios assuming chromatid segregation for both the Ms and Rt loci. The gene frequency of parallel spindles was estimated in the 4x population as 0.74.     

Yield and tuber characteristics of 4x progeny from 2x×2x crosses

Summary Unrelated, unselected 2x haploid-species hybrids that produce 2n eggs, by second division restitution and 2n pollen due to first division restitution were intercrossed to generate 4x progeny. The 19, 4x families were compared with seven cultivars for tuber yield, tuber appearance and tuber set. The mean yield of the 4x families was 30% higher than the mean yield of the cultivars. The best five 4x families outyielded the best five cultivars by 57% and 69% at two locations. Cultivars were superior for tuber appearance and tuber set. The high yields of the 4x families are due to genetic diversity of the 2x parents and their ability to transmit that diversity to the 4x progeny utilizing 2n gametes. The potential of the 2x×2x breeding method is dependent on developing 2x hybrid clones that form 2n eggs and possess desirable tuber types; clones producing 2n pollen and good tuber quality are available.     

Seed set in 4x x 2x crosses as related to 2n pollen frequency

Seeds per fruit following 4x × 2x crosses in potato are roughly related to the frequency of 2n pollen. Our goal was to examine precisely the relationship between frequency of stainable 2n pollen and seeds per fruit (s/f) in 4x × 2x crosses. A 4x cultivar with high female fertility and 21 2n pollen producing 2x hybrids were used as seed and pollen parents, respectively. 2n pollen frequencies varied from 1 to 99% in the 2x hybrids and seed set ranged from 0 to 305 s/f in 4x×2x crosses. Mean seeds per fruit increased in response to increases from 1 to 50% 2n pollen, but did not increase in response to using a pollen sample with a 2n pollen frequency over 60%. Seed set averaged 11 s/f corresponding to pollen samples with 1–5% 2n pollen, 50 s/f at 10–20%, 125 s/f at 20–30%, and over 170 s/f at 2n pollen frequencies over 60%. Seed set in 210 control 4x × 4x crosses indicated that equivalent seed set occurs in 4x × 2x crosses when 2n pollen frequencies are over 20–30%. The 2x hybrids differed in mean and variation of 2n pollen frequencies and seed set in 4x × 2x crosses. One 2x hybrid with a meiotic aberration (sy-3) resulting in all univalents at Metaphase I (ordinarily leading to male sterility) and parallel spindles (ps) at Anaphase II had close to 100% 2n pollen (of the stainable pollen) and gave equivalent s/f in 4x × 2x crosses to s/f in 4x × 4x crosses. It is apparent that ample seed set occurs for using the 4x × 2x breeding scheme with 2n pollen frequencies over 10% and that even very low 2n pollen frequencies (1–10%) provide seed for the 4x×2x breeding approach.     

Performance and stability of nine 4x clones from 4x−2x crosses and four commercial cultivars

Summary Nine clones from 4x−2x crosses were evaluated along with four cultivars in six Wisconsin environments. The 4x clones from 4x−2x crosses had as their 2x parents hybrids with haploid Tuberosum and either Group Phureja orSolanum tarijense. The 2x hybrids produced 2n pollen by first division restitution. The traits evaluated were marketable yield, mass density and chip color. Stability analysis was conducted by determining the linear relationships between mean yield of individual clones and environmental mean yields. Mean square deviations from linear regression (s² _d) were used to evaluate phenotypic stability and regression coefficients (b) as environmental response parameters. Three 4x clones from 4x-2x crosses were more stable and not significantly different for yield than cv. Atlantic; some also had superior specific gravity and chip color. The results suggest that the 4x×2x breeding method is very efficient for the production of high yielding, stable clones with superior processing qualities, particularly since the 4x clones from 4x-2x crosses originated from very small source populations.     

Comparisons between 4x×2x hybrid and open-pollinated true-potato-seed families

Summary TPS progenies from open-pollinated and 4x×2x crosses were compared on the basis of seed quality, seedling vigor, seedling tuber production and tuber yield. The hybrids from 4x×2x crosses were superior in all the traits. Even though the hybrid families may have these outstanding features, the relatively high cost of producing seeds can be a limitation to their widespread utilization in developing countries. Seeds from open pollination are much less expensive; their cost of production is only 10–20 % of that of hybrid seeds. Thus, the use of TPS families from open pollination may be an economical method for the production of potatoes from true seed until a suitable method of producing low-cost hybrid seed is available.

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Zusammenfassung Die Hauptgruppen von Kartoffelsamen-Familien (TPS, ‘true-potato-seed’) die für eine Kartoffelproduktion verwendbar erscheinen, sind: a) Hybriden von 4x×2x-, 2x×4x- und 2x×2x-Kreuzungen (Peloquin, 1982) sowie 4x×4x-Kreuzungen (Peloquin, 1979; Mendoza, 1979), b) offen best?ubende Nachkommenschaft. Diese beiden Gruppen von TPS-Nachkommenschaften haben deutlich unterschiedliche Eigenschaften im Hinblick auf ihre Eignung für die Kartoffelproduktion. Zweck dieser Studie war ein Vergleich zwischen TPS-Nachkommen einerseits und 4x×2x-Kreuzungen und offen best?ubenden andererseits auf der Basis von Saatqualit?t, S?mlingsvitalit?t, S?mlingsknollen-Produktion und Knollenertrag. Zwei-und-fünfzig TPS-Familien, 35 von offen best?ubenden und 17 von 4x×2x-Kreuzungen wurden verwendet. Die Hybridfamilien entstanden aus Kreuzungen zwischen tetraploiden Klonen und 2x Phureja-haploiden Tuberosum-Hybriden mit der F?higkeit zur Erzeugung von 2n-Pollen durch FDR. Mit wenigen Ausnahmen entstanden alle OP-Nachkommen aus denselben tetraploiden Eltern, die in den 4x×2x-Kreuzungen verwendet wurden. S?mtliche Samen- und S?mlingstests liefen im Laboratorium und im Gew?chshaus. Die S?mlinge für die Feldversuche wurden im Gew?chshaus angezogen und dann im Alter von etwa 6 Wochen in das Feld ausgepflanzt. Alle Ertragsversuche wurden mittels RCBD und 2 Wiederholungen durchgeführt. Die Ergebnisse zeigen betr?chtliche Unterschiede bei Samengr?sse, Keimungsrate, S?mlings-Vitalit?t und S?mlings-Knollenproduktion zwischen den 4x×2x-Hybriden und OP-Nachkommen (Tabellen 1 und 2). Die Hybriden-Nachkommen waren bei allen diesen Merkmalen besser. Desweiteren erkl?ren die mittleren Knollenertr?ge der beiden Gruppen von TPS-Familien die überlegenheit der 4x×2x-Familien (Tabelle 3). Die Heterosis-Reaktion in den Nachkommen der 4x×2x-Kreuzungen wird auf der Basis der FDR-Weise für 2n-Pollenbildung erkl?rt. Bei diesem Mechanismus wird mehr als 80 Prozent der Heterozygotie der 2x-Eltern auf die Nachkommen übertragen. Ungeachtet der noch ausstehenden Eigenschaften der Hybrid-Familien k?nnten die relativ hohen Kosten für die Hybridsaat-Produktion eine Begrenzung für eine verbreitete Verwendung in Entwicklungsl?ndern bedeuten. Folglich kann die Verwendung von TPS-Familien von Offen-Best?ubenden eine ?konomische Methode für die Produktion von Kartoffeln aus Samen sein, bis eine brauchbare Methode zur kostengünstigen Produktion von Hybridsamen vorhanden ist.

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Résumé Les graines recherchées pour la production directe de pommes de terre proviennent des principaux types de familles suivants: a) les hybrides obtenus par croisément 4x×2x, 2x×4x, 2x×2x (Peloquin, 1982) et 4x×4x (Peloquin, 1979; Mendoza, 1979), b) les descendances issues de la pollinisation naturelle. Les lignées de ces deux groupes ont des caractéristiques distinctes sur le plan de leur aptitude à produire des pommes de terre. Le sujet de cette étude a été de comparer les descendances issues du croisement 4x×2x et celles provenant de la pollinisation naturelle, en se basant sur la qualité des semences, la vigueur germinative, la production de tubercules et le rendement en tubercules. Cinquante-et-deux familles, dont 35 issues de pollinisation naturelle et 17 du croisement 4x×2x ont été utilisées. Ces dernières étaient obtenues par le croisement entre cl?nes tétraplo?des et des hybrides Phureja 2x×Tuberoseum haplo?de capables de produire du pollen 2n. A quelques exceptions près, toutes les lignées issues de pollinisation naturelle étaient issus des mêmes parents tétraplo?des utilisés dans les croisements 4x×2x. Tous les tests sur graines et de germination étaient effectués en laboratoire et en serre. Les semences pour les essais au champ étaient réalisées en serre puis les plantes étaient transplantées dans le champ après six mois de croissance, selon un dispositif RCBD à 2 répétitions. Les résultats obtenus montrent des différences importantes au niveau de la taille des graines, des pourcentages de germination, de la vigueur germinative et de la production de tubercules entre les hybrides 4x×2x et les lignées issues de pollinisation naturelle (tableaux 1 et 2). La descendance des hybrides étaient meilleure pour tous les caractères. Le rendement moyen en tubercules dans les deux groupes souligne la supériorité des familles de 4x×2x (tableau 3). Le comportement des lignées 4x×2x s'explique par le mode de formation du pollen 2n. Dans ce mécanisme, plus de 80 pour cent de l'hétérozygotie du parent 2x est transmis à la descendance. En dépit des caractéristiques intéressantes des familles d'hybrides, leur co?t relativement élevé peut être une limite à la diffusion dans les régions de grande culture. Par conséquent, l'utilisation de graines issues de pollinisation naturelle peut être économique pour la production de pomme de terre jusqu'à ce qu'une méthode de création d'hybrides moins onéreuse soit mise au point.

     

Erwinia resistance in backcross progenies ofSolanum tuberosum x S. tarijense andS. tuberosum (+) S. commersonii hybrids

Summary The resistance to tuber soft rot caused byErwinia carotovora ofSolanum tuberosum x S. tarijense andS. tuberosum (+) S. commersonii hybrids and their backcrosses is reported. A number of resistant diploid sexual hybrids and tetraploid/hexaploid somatic hybrids were selected. Backcross progenies were obtained through 2x×4x crosses involving a resistant diploid hybrid and tetraploidS. tuberosum, and through 4x×4x crosses between a resistant somatic hybrid andS. tuberosum. The hybrids showed high variability interms of resistance to tuber soft rot. The resistance of progeny from 2x×4x backcrosses was similar to that of the parental sexual hybrid. By contrast, the resistance of genotypes deriving from 4x×4x backcrosses was reduced compared with the resistant somatic hybrid. In general, tuber characteristics of the backcross hybrids improved considerably as compared with their parents, and tuber yield per plant was good.     

2n pollen in eleven 2x, 2EBN wild species and their haploid x wild species hybrids

Summary Sixty-three plants producing 2n pollen were identified among 65 introductions of 11 2x, 2EBN wild species. They were found in 27 of the 65 introductions representing ten of 11 species. The gene frequencies for the allele controlling 2n pollen formation ranged from 0.19 to 0.65. Seventyeight haploid x wild species hybrid families were produced using the previously identified 2n pollen plants as male parents. One hundred and thirty-two plants that produced 2n pollen were identified among the haploid x wild species hybrids at one location and 44 at another. The high number of haploid x wild species hybrids that produced 2n pollen and the large number of hybrids with acceptable pollen stainability demonstrate the potential of the hybrids in 4x × 2x germplasm transfer. Potato breeders can unleash the genetic diversity present in the 2x, 2EBN wild species by screening them for 2n pollen and crossing the 2n pollen producing plants to haploids.     

Breeding for 2n egg production in haploid × species 2x potato hybrids

The identification of diploid(2x), Tuberosum haploid × wild species hybrids (HS) which produce high frequencies of 2n eggs and have good tuber appearance is important for obtaining 4x progeny from 2x × 2x crosses in potato. More than 1700 HS clones were screened for the occurrence and frequency of 2n eggs through 2x × 4x crosses during two pollination periods. The resulting seed/fruit provides an estimate of 2n egg frequency. About 650 HS clones produced 2n eggs; 63 had 10–114 seeds/fruit; and 27 were selected for good tuber type. There was a large variation in seed set after 2x × 4x crosses, both within and between clones. Comparison of fruit and seed set between the two pollination periods using the same 595 clones indicated that environmental factor significandy affected 2n egg frequency. The mode of 2n egg formation was mainly due to omission of the second meiotic division controlled by a recessive gene (os). The gene frequency foros varied from 0.28 to 0.76 among six, 2x taxa. Both additive and dominance variance were significant for seed set after 2x × 4x crosses. Narrow sense heritability was estimated as 0.24. The average degree of dominance was equal to 1.66 which could indicate overdominance. Alternatively, this could be due to linkage disequilibrium,i.e. pseudooverdominance. However, dominance variance was greater than the additive variance indicating recurrent selection can be useful for improving the frequency of 2n egg production in the 2x population. The selected individuals, based on their phenotypic performance, should be progeny tested to identify the best parents for use in the next cycle of recombination.     

Performance of haploid x wild species, 2x hybrids (involving five newly evaluated species) in 4x × 2x families

The 4x × 2x breeding scheme in potato allows introgression of germ-plasm from the 2x wild species into the cultivated tetraploid. Eighteen 4x × 2x, forty-five 4x × 4x, seven 4x-selfs, and five open pollinated (OP) families were transplanted in a randomized complete block design with two replications and 18 plants per family per replication. The 2x parents of the 4x × 2x families were seven haploid x wild species hybrids. These hybrids involve five 2x, wild species,Solanum bukasovii, S. gourlayi, S. muhidissectum, S. vermi, andS. verrucosum, which had not previously been evaluated in the 4x × 2x breeding scheme. Data were recorded for family yield, maturity, tuber uniformity, tuber number, and general tuber appearance. The 4x × 2x families as a group performed as well as or better than the 4x × 4x, 4x-self, and 4x-OP groups for all traits except maturity. Within family maturity distributions for 4x × 2x families indicate the possibility to select early maturing clones from high yielding families. Eleven of the fifteen families in the top 25% of the 4x × 2x and 4x × 4x families for yield were 4x × 2x families. Three of the four 2x parents evaluated for parental performance gave highly significant responses for increased yield. 4x × 2x families with Chiquita as a parent were the poorest yielding while several of the 4x x 4x families of which it was a parent were among the highest yielding: This indicates that the benefits of maximum heterozygosity may be overridden if the percentage of unadapted germplasm is too high.