Mexican Cultivars Research Articles

Diversity of Unavailable Polysaccharides and Dietary Fiber in Domesticated Nopalito and Cactus Pear Fruit (Opuntia spp.)

The aim of this study was to quantify mucilages, pectins, hemicelluloses, and cellulose of nopalitos (edible, as vegetable, young cladodes of flat-stemmed spiny cacti) of most consumed Mexican cultivars, and sweet and acid cactus pear fruits of Opuntia spp. The hypothesis is that, regardless of their unavailable polysaccharides diversity, nopalitos and cactus pear fruits are rich sources of soluble and insoluble dietary fiber. Twelve cultivars of Opuntia spp. were used. Nopalitos had a significant variation in structural polysaccharides among the cultivars: mucilages (from 3.8 to 8.6% dry matter (DM)) averaged near a half of pectins content (from 6.1 to 14.2% DM) and tightly bound hemicelluloses (from 2.2 to 4.7% DM), which were the less abundant polysaccharides, amounted 50% of the loosely bound hemicelluloses (from 4.3 to 10.7% DM). Acid fruits (or 'xoconostle') had significantly higher unavailable polysaccharides content than sweet fruit, and contain similar proportions than nopalitos. Unavailable polysaccharides represent a high proportion of dry tissues of nopalitos and cactus pear fruits, composition of both of these soluble and insoluble polysaccharides (total dietary fiber) widely vary among cultivars without an evident pattern. Nopalitos and cactus pear fruit can be considered an excellent source of dietary fiber.

Genetic Relatedness of Mexican Common Bean Cultivars Revealed by Microsatellite Markers

ABSTRACTMexico has various types of common bean (Phaseolus vulgaris L.) and a long history of breeding in multiple commercial classes. In this study, our goal was to evaluate a wide collection of commercial cultivars of common beans from Mexico, including Azufrado, Bayo, Flor de Mayo, Flor de Junio, Pinto, and black bean types, to discover their level of relatedness with 32 simple sequence repeat (SSR) markers. Eight panels of end‐labeled fluorescent SSR loci were used in an automated detection system and 85% of loci were read. A total of 204 alleles were detected in the study, showing the diversity among the Mexican cultivars. Through population structure and principal components analyses, Andean and Mesoamerican genotypes as well as three subgroups within the Mesoamerican genepool were distinguished. The divisions corresponded to a group of Andean cultivars, two subgroups of the Durango–Jalisco (DJ) complex, and one group equivalent to race Mesoamerica. This latter race was much less diverse than the DJ complex and had little gene flow with other groups. This study shows the value of fluorescent SSR markers for evaluating commercial cultivars of common beans. Given the importance of Mexico as a primary center of origin for common beans, as a major market for the crop, and as the second largest producer in Latin America, this study has implications for the global evaluation of common bean cultivars.

Ancient DNA confirms a local origin of domesticated chenopod in eastern North America

Domesticated chenopod was an important starchy seed crop in eastern North America before the rise of maize agriculture. Domesticated chenopod first appeared in North America during the fourth millennium B.P., however its wild progenitor and site of domestication remain unresolved. Archaeological evidence suggests a local domestication in the Eastern Woodlands, while morphological similarities with modern Mexican cultivars indicate a possible introduction from Mesoamerica. To distinguish between these two scenarios, we isolate chloroplast DNA (cpDNA) from modern and archaeological North American chenopods sampled from across their geographic range. Our results demonstrate that the chenopod grown in the Eastern Woodlands was locally-derived, indicating that independent domestication events gave rise to the ancient eastern North American and modern Mexican cultivars. These results strengthen the argument for an entirely native pre-maize crop complex with chenopod as a major component.

Sunflower domestication alleles support single domestication center in eastern North America

Phylogenetic analyses of genes with demonstrated involvement in evolutionary transitions can be an important means of resolving conflicting hypotheses about evolutionary history or process. In sunflower, two genes have previously been shown to have experienced selective sweeps during its early domestication. In the present study, we identified a third candidate early domestication gene and conducted haplotype analyses of all three genes to address a recent, controversial hypothesis about the origin of cultivated sunflower. Although the scientific consensus had long been that sunflower was domesticated once in eastern North America, the discovery of pre-Columbian sunflower remains at archaeological sites in Mexico led to the proposal of a second domestication center in southern Mexico. Previous molecular studies with neutral markers were consistent with the former hypothesis. However, only two indigenous Mexican cultivars were included in these studies, and their provenance and genetic purity have been questioned. Therefore, we sequenced regions of the three candidate domestication genes containing SNPs diagnostic for domestication from large, newly collected samples of Mexican sunflower landraces and Mexican wild populations from a broad geographic range. The new germplasm also was genotyped for 12 microsatellite loci. Our evidence from multiple evolutionarily important loci and from neutral markers supports a single domestication event for extant cultivated sunflower in eastern North America.

Soil texture effects on the development of Jatropha seedlings – Mexican variety ‘piñón manso’

There is considerable disagreement on the effects of different soil conditions on the growth of Jatropha curcas L., although different reports agree on some factors, such as a preference for sandy soils over clay soils. This paper presents results on the growth of seedlings of a low-toxic Mexican cultivar in three different soils from the SE of Mexico. The Mexican seeds were sown in soils of different textures: sandy, sandy-loam and clay-loam. The germinated seedlings were monitored during a period of one month. Then, they were uprooted to record below and above ground morphological parameters and dry matter weight. Stem lengths, root collar diameter, length and diameter of the five main roots, number of true leaves and dry matter were analyzed using one-way ANOVA. The soils used were subjected to a chemical analysis to determine soil nutrient contents, which revealed that clay-loam soil had the highest nutrient content, followed by the sandy-loam, while sandy soil presented the lowest values. It was found that seedlings grown in sandy-loam soil were significantly taller than those in clay-loam and sandy substrates (P <= 0.05). Root collar diameter, root diameter, number of true leaves and dry matter weight did not present significant differences between plants grown in sandy-loam and clay-loam soils, however they showed significant differences when compared with plants grown in sandy soil. Therefore it can be concluded that development of seedlings in sandy-loam soils was greater, followed by those in clay-loam, while the poorest performance of the seedlings was recorded in sandy soil. Published by Elsevier Ltd.

Physicochemical, Textural, and Nutritional Characterization of Mexican Rice Cultivars

ABSTRACTThe physicochemical properties, textural properties, and starch digestibility of rice cultivars grown in Mexico were evaluated. Variations existed in grain dimensions, and the rice grains were classified as medium, long, and extra long. Huimanguillo had the highest amylose content (30.4%), and A06, A92, A98, and Champoton presented the lowest amylose content (24.3–25.2%). The protein content was 7.1–11.0% and the lipid level was 0.47–1.22% among these Mexican cultivars. Champoton showed the highest temperature and enthalpy of gelatinization, and this with A98, Culiacan, and Huimanguillo had the highest enthalpy of retrogradation. Cotaxtla had the highest pasting peak, setback, and final viscosity. The texture assessment in cooked rice showed that A06 had the highest hardness, and A96 and A98 had the highest stickiness. There was little difference in the rapidly digestible starch, slowly digestible starch, and resistant starch content of tested Mexican rice cultivars. The differences in the physicochemical properties could be used to determine the end use of these Mexican rice cultivars.

Molecular evidence and the origin of the domesticated sunflower

In their article on the history of domesticated sunflower in Mexico, Lentz et al. (1) claim that two recent molecular genetic studies (2, 3) failed to examine indigenous Mexican cultivars. In fact, two such cultivars, maiz de teja and maiz negro (2, 3), were included in both studies. These cultivars were purchased in Teocaltiche, Jalisco, by Carl O. Sauer and are considered “without much doubt” to represent indigenous strains (4). In addition to their Mexican provenance, achenes from both cultivars exhibit a “beak” shape that is absent in cultivated material from outside of Mexico (4). Despite their unique phenotype, these Mexican cultivars were inferred to have arisen from wild populations within the east–central United States with >98% confidence based on nuclear microsatellite data (2). They also had the chloroplast DNA haplotype that is characteristic of domesticates from the United States (3). Thus, it is clear that they were derived from the same domestication event in eastern North America (5) that produced all other sunflower cultivars examined to date (2, 3). Although we have previously noted that such analyses cannot exclude the possibility of a second, unsampled origin of domestication (2, 3), the available molecular data are indicative of a single origin outside of Mexico. Given the relatively young age of the latest discoveries (≈290 cal B.C.) and the possibility of dissemination from eastern North America accompanied by ongoing selection for increased achene size, it seems premature to conclude that there was a second origin of sunflower domestication.

Patterns of introduction and diversification of Vanilla planifolia (Orchidaceae) in Reunion Island (Indian Ocean)

The cultivated species Vanilla planifolia is a typical example of a crop introduced from its area of origin (America) to new regions where natural pollinators are absent. Although the Vanilla cultivars are exclusively vegetatively propagated, a high degree of phenotypic variation is observed among the cultivars in their introduction areas such as Reunion Island. To test several hypotheses explaining this variation-different introduction events, somatic mutations and sexual reproduction (through manual pollination)-we used AFLP markers to elucidate the patterns of introduction of V. planifolia. Most of the accessions cultivated in the world were derived from a single accession, possibly the Mexican cultivar Mansa. The patterns of diversification of this cultivated species were also studied and compared with other cultivated (V. tahitensis) and wild (V. pompona and V. bahiana) species. Except for one particular phenotype ('Aiguille'), which may come from sexual reproduction, cultivated accessions exhibit very low levels of genetic diversity. They have evolved by the accumulation of point mutations through vegetative multiplication. The genetic diversity revealed could not explain the phenotypic diversity, which may be related to epigenetics or polyploidy. This new understanding of the basis of genetic diversity of vanilla may assist to improve management of genetic resources.

THE QUALITY OF VEGETABLE OIL FROM THREE VARIETIES OF SUNFLOWER SEEDS (HELIANTHUS ANNUUS)

ABSTRACT Vegetable oils become susceptible to oxidation during their processing. The appropriate extraction and refining conditions of oil from two experimental cultivars (Madero‐91 and Cianoc‐2) of sunflower seeds and a commercial one (Victoria) as a control, were studied. Isopropyl alcohol was used in the extraction and refining, and compared with hexane. The refining was performed by the miscella method at 40, 50, 60 and 70%. Free fatty acids (FFA) and malonaldehyde analysis of crude oils afforded no significant differences among solvents and sunflower varieties. In refined oils, differences found with the miscella concentration, the malonaldehyde content and FFA content were not significant. Cianoc‐2 was the best source for oil production because of its lower values in FFA and malonaldehyde content.PRACTICAL APPLICATIONSThe use of hexano in refining vegetable oil in Mexico is common, lack of knowledge about the use of new solvents and their impact on the processing conditions with sunflower seed cultivars is lack. The present work describes at lab scale, the work conditions, advantages and posibilities and limitations of the use on isopropyl alcohol in comparison with hexane and the use of three Mexican cultivar with this approach, with emphasize in oxidation conditions of refined vegetable oil.

Effect of photoperiod and temperature on resistance againstPhytophthora infestans in susceptible and resistant potato cultivars: Effect on deposition of structural phenolics on the cell wall and resistance to penetration

Deposition of phenolic compounds before and after inoculation with Phytophthora infestans was evaluated in two Mexican cultivars (Malinche and Tollocan) with major unknown R genes for resistance to potato late blight, two cultivars (393295.236 = CIP1 and 391046.22 = CIP2) without R genes from the International Potato Center (CIP) and the susceptible cultivar Atlantic. Before inoculation, plants were grown in growth chambers at two temperatures (16 or 24 C) and two photoperiods (PPD 12 or 16 h day length). Forty-eight hours after inoculation, the number of penetrations was recorded and depositions of phenolic compounds were classified according to detection and location in (a) the anticlinal cell wall, (b) the whole cell, (c) the stomatal cells, and (d) without detectable depositions of phenolic compounds. The concentration of phenolic compounds in the epidermal cells was slightly increased at 16 C and 16 h PPD and penetration frequency was lower at 16 C (12 h PPD). Concentration of phenolic compounds was not correlated with penetration frequency, but was correlated with the resistance level of the different potato cultivars. Atlantic had the highest number of penetrations followed by Tollocan, CIP1, CIP2, and Malinche. The cytological observations indicated that four types of deposition of phenolic compounds occurred in all five potato cultivars irrespective of their type and level of resistance. These results suggest that deposition of phenolic compounds on epidermal cells is a general resistance mechanism in potato leaves that does not have a specific relation with resistance to the penetration of P. infestans. Phenolic depositions were intrinsically similar in potato cultivars with and without R genes, which stresses the difficulty in differentiating between horizontal and vertical resistance.

Effect of temperature and photoperiod on symptoms associated with resistance toPhytophthora infestans after leaf penetration in susceptible and resistant potato cultivars

The effect of temperature and photoperiod on the expression of resistance against Phytophthora infestans in five potato cultivars with and without resistance (R) genes was investigated. Four experiments were carried out under controlled conditions in growth chambers. Two cultivars (393295.236 and 391046.22) without known R genes from the International Potato Center (CIP) in Lima, Peru, two Mexican cultivars with major R genes (Tollocan and Malinche), and a susceptible cultivar (Atlantic) were used in this study. Plants were grown for 32 days in growth chambers at two temperatures (16 and 24 C) and two photoperiods (12 and 16 h day length), then inoculated with a compatible isolate of P. infestans and incubated in a mist chamber at 18 C. The inoculation efficiency, the percentage of lesions that did not grow beyond the inoculation spot, the sporangia density, and the AUDPC were recorded. The percentage of arrested lesions decreased with temperature in the two most resistant cultivars (393295.236 and Malinche), and the AUDPC was lower at 16 than at 24 C in four of the five cultivars. The inoculation efficiency and the sporangia density were not affected by change in temperature. Sporangia density increased at 16 h photoperiod; however, the final infected leaf area was not affected. Our results demonstrate that the expression of horizontal and vertical resistance was affected by temperature; however, the relative resistance ranking among cultivars was the same in the four experiments with different temperatures and photoperiods. It is assumed that the resistance in the Mexican cultivars may be conferred by minor resistance genes and by the residual effect of defeated R genes. These results emphasize the difficulty in differentiating between horizontal and vertical resistance.

Genetic Variability and Relationship of Closely Related Spanish Traditional Cultivars of Tomato as Detected by SRAP and SSR Markers

We studied the genetic variability of some traditional tomato (Lycopersicon esculentum L. Mill.) cultivars of Spain, and established their relationships using both simple sequence repeats (SSR) and sequence related amplified polymorphism (SRAP) markers. These included cultivars from different locations of three main types, Muchamiel, De la pera, and Moruno. Additionally we tested two other local cultivars, `Valenciano' and `Flor de Baladre', plus a small sample of commercial cultivars and a few wild species. Both types of markers resolved the cultivars from different groups, but SSR failed to distinguish some of those classified under the same group. All the De la pera cultivars clustered together by genetic similarity with the SRAP markers. The other traditional cultivars, which are grown in a wider geographic range, formed a more diffuse group, which included the commercial cultivar Roma. The Mexican cultivar Zapotec, a breeding line, and the virus-resistant commercial hybrid `Anastasia' were the most distant of all the cultivars. The latter hybrid had higher similarity to the wild species due to introgressed segments from them carrying the resistance genes. Similar results were observed for SSR markers but with a lower level of resolution. This information would be useful to facilitate tomato germplasm conservation and management efforts.

The Genetic Anatomy of a Patented Yellow Bean

Since a 1980 Supreme Court decision, it is possible in the USA to obtain a utility patent for crop cultivars and other life forms. Furthermore, it is also possible to obtain Plant Variety Protection (PVP) for a cultivar. Among the awards of the United States Patent and Trademark Office and the USDA Plant PVP Office are a utility patent and a PVP certificate, respectively, associated with a yellow‐seeded bean (Phaseolus vulgaris L.), specifically the cultivar Enola. These awards have been controversial because of, among several reasons, the perceived lack of novelty of the yellow seed color and the cultivar itself. To check the origin of Enola, we fingerprinted a representative sample of 56 domesticated common bean accessions, including a subsample of 24 cultivars with yellow seeds similar to those of Enola. Fingerprinting was accomplished with amplified fragment length polymorphisms (AFLP). Five EcoRI/MseI and five PstI/MseI primer combinations were used, which revealed 133 fragments. The PstI/MseI primer combinations revealed a 3‐fold larger number of polymorphic markers than the EcoRI/MseI primer combinations. Most yellow‐seeded beans, including Enola, were included in a tightly knit subgroup of the Andean gene pool. Enola was most closely related to the pre‐existing Mexican cultivar Azufrado Peruano 87. A sample of 16 individuals of Enola displayed a single 133‐AFLP‐fragment fingerprint, which was identical to a fingerprint observed among yellow‐seeded beans from Mexico, including Azufrado Peruano 87. Probability calculations of matching the specific Enola fingerprint showed that the most likely origin of Enola is by direct selection within pre‐existing yellow‐bean cultivars from Mexico, most probably ‘Azufrado Peruano 87’.

AFLP assessment of diversity in sweetpotato from Latin America and the Pacific region: Its implications on the dispersal of the crop

Although originally domesticated in tropical America, the sweetpotato [Ipomoea batatas (L.) Lam.] has a long history of cultivation in the Pacific region. While the post-Columbus dispersal of sweetpotato to Asia and the Pacific is well documented, the hypothesis that there was a prehistoric transfer of sweetpotato by Peruvian or Polynesian voyagers from Peru to Oceania has long been a controversial issue. The objective of this study was to assess the genetic diversity and interrelationships of sweetpotato landraces from the Pacific region and Latin America, and test the hypothesis of human transfer of this crop to the Pacific Island in prehistoric times. Seventy-five sweetpotato landraces from Peru, Ecuador, Mexico, the Philippines, Papua New Guinea (PNG) and 5 Oceania countries were analyzed using amplified fragment length polymorphism (AFLP). Multidimensional scaling (MDS) and analysis of molecular variance (AMOVA) revealed a large genetic variation in the Oceania gene pool, far greater than that in Peru-Ecuador. The Mexican cultivars were grouped together with those of Oceania. In contrast, there is little association between the Peru-Ecuador germplasm and that of Oceania. These results suggest that Peru-Ecuador may not be the source of the Oceania sweetpotato germplasm. Natural dispersal from Mesoamerica is an alternative explanation, to the ‘Kumara hypothesis’, for the origin of the Oceania sweetpotato.

Potato Late Blight Management in the Toluca Valley: Field Validation of SimCast Modified for Cultivars with High Field Resistance.

Management of potato late blight in the highland tropics is very costly and remains difficult. Reducing the impact of late blight through the use of resistant cultivars in combination with a fungicide forecasting system could lower the number of costly fungicide applications. Previously, we evaluated the fungicide advisory SimCast for use with Mexican cultivars of high levels of field resistance for use in the central highlands of Mexico and found that it predicted too many fungicide applications for cultivars of moderate to high levels of resistance. We adapted SimCast for cultivars with higher levels of resistance, and field validations conducted in 1999 and 2000 show that SimCast resulted in good disease control on cultivars ranging from susceptible to highly resistant. The number of fungicide applications forecast for cultivars with moderate to high levels of resistance was reduced. Precipitation was the environmental variable responsible for most of the forecasts made. Our work demonstrates that a predictive system can be portable from the temperate climate to a tropical highland climate. A user-friendly decision support system consisting of just a rain-gauge and the exclusive use of SimCast's fungicide units could be a valuable and affordable tool in managing potato late blight in the highland tropics.

Potato Cultivars from the Mexican National Program: Sources and Durability of Resistance Against Late Blight

ABSTRACT The Mexican National Potato Program has produced several cultivars with high levels of field resistance. We evaluated the durability of resistance to potato late blight of a selection of 12 such cultivars using data from 1960 to the present. Data were extracted from the field notebooks located in the archives of the Mexican National Potato Program in the John S. Niederhauser Library in Toluca, Mexico. There was a trend indicating that field resistances to potato late blight of Mexican cultivars released between 1965 to 1999 were durable. At least two of the cultivars, namely 'Sangema' and 'Tollocan', have been grown on at least 4 to 5% of the potato acreage and over long periods of time without decay in levels of field resistance. Pedigrees of the 12 cultivars indicate that most of the field resistance was introgressed from Solanum demissum. Field resistance might also be derived from commonly grown land-race cultivars such as 'Amarilla de Puebla' and 'Leona'. These have been grown in Mexico since about the 1780s. They have the appearance of S. andigena-derived material but their genetic background is unknown.

Physicochemical Characterization of Starches from Amaranthus Cruentus Grains

The physicochemical properties of starches isolated from three cultivars (Mexican, African and A200D) of Amaranth cruentus grains were studied. The yield of starch was in the range 29–38.3% on a whole grain basis. The starch granules were polygonal with smooth surfaces. The granule size was in the range 0.75–1.5 μm for all three cultivars. The free, bound and total starch lipids ranged from 0.05 (b 0.07%, from 0.16 to 0.28 and from 0.20 to 0.35%, respectively. The total amylose content ranged from 3.9 to 5.7% of which 10.3 to 15.8% were complexed by native lipid. The X-ray pattern was of the “A” type. The intensities of the major diffraction patterns followed the order: Mexican > African > A200D. The swelling factor followed the order: A200D > African > Mexican. All three starches exhibited identical pasting temperatures. However, they differed with respect to the highest viscosity reached during the heating cycle (Mexican > A200D > African), viscosity at 95°C (Mexican > A200D > African), the extent of breakdown (African > A200D ∼ Mexican) in viscosity (during the holding cycle at 95°C) and setback (A200D > African > Mexican). The gelatinization temperature ranges were 72.2–91.0°C (Mexican), 69.8–84.1°C (African) and 69.0–83.6°C (A200D). The enthalpy of gelatinization (J g−1) were: 11.8 (Mexican) 12.3 (African) and 14.5 (A200D). The extent of acid hydrolysis (2.2 N HCl at 35°C) followed the order: A200D > African > Mexican. The susceptibility of the starches towards hydrolysis by porcine pancreatic α-amylase followed the order: African > A200D > Mexican. The freeze-thaw stability followed the order: Mexican > African > A200D. The results of this study showed that bonding forces within the amorphous and crystalline regions are most pronounced in the Mexican cultivar.

MELHORAMENTO DO TRIGO: XXXI. HERDABILIDADES E CORRELAÇÕES ENTRE TRÊS CARACTERÍSTICAS AGRONÔMICAS EM POPULAÇÕES HÍBRIDAS

Para estimar a herdabilidade, em sentido amplo e restrito, para altura de planta, número de grãos por espigueta e produção de grãos, bem como as correlações entre essas características, realizaram-se cruzamentos entre o `BH-1146' (P1), de origem nacional e porte alto, com os cultivares mexicanos CMH 80.638/ CMH 75A. 411//CMH 80.638 (P2); CMH 79.959/2 * CNO 79 (P3) e CMH 79.481/CMH 77A. 917 (P4), de porte baixo a médio. Plântulas, das gerações parentais F1 e F2 e dos retrocruzamentos, para ambos os pais, foram transplantadas para vasos no telado. Para o caráter altura de planta, os valores estimados para as herdabilidades em sentido amplo e restrito, ao nível de plantas individuais, foram altos em todos os cruzamentos, variando de 0,86 a 0,91 e de 0,77 a 0,96 respectivamente. Para o caráter número de grãos por espigueta, os valores da herdabilidade em sentido amplo (0,26 a 0,50) e restrito (0,26 a 0,61) variaram, conforme o cruzamento, de baixo a médio. Dados da herdabilidade em sentido amplo para produção de grãos variaram de médio a alto (0,63 a 0,70) e, em sentido restrito, foram médios (0,41 a 0,62). As correlações fenotípicas entre produção de grãos e altura de planta foram significativas para os cruzamentos P1 x P3 (-0,19 P &lt; 0,05) e P1 x P4 (0,62 P &lt; 0,01) e não significativa para P1 x P2 (0,06). Correlações fenotípicas entre produção de grãos e número de grãos por espigueta (P1 x P3 e P1 x P4), e entre altura de plantas e número de grãos por espigueta (P1 x P2 e P1 x P4) foram positivas e significativas. Os resultados sugerem ser possível, no cruzamento P1 x P3, selecionar plantas mais produtivas, de porte médio a baixo e com maior número de grãos por espigueta.

Developmental Responses by Tall and Dwarf Isogenic Lines of Spring Wheat to Applied Gibberellins.

Tall (rht) and dwarf (Rht) isogenic lines of two Mexican spring wheat cultivars were grown at 25/20�C day/night in short (8 h) days of either natural or artificial light to determine their relative stem, leaf and flowering responses to one or two long days, 11 different gibberellins (GAs) and the growth retardant Cycocel (CCC). Although stem and leaf elongation in the dwarf lines did not respond to a GA application, inflorescence initiation and development was enhanced by several GAS, reduced by CCC, and restored by subsequent GA application. The floral response of tall lines to GAs was greater than that of the dwarf lines, whereas the reverse was the case with their exposure to long days. These results suggest that endogenous GAs are involved in the floral induction of wheat, and that although the stems and leaves of dwarf lines may not be able to respond to exogenous GAs, their shoot apices can do so and are sensitive to endogenous GA levels.

High Temperature Stress in Wild Wheats and Spring Wheats

The effect of high temperature stress on wild and spring wheats is reviewed. Wild wheats include species in the genera Aegilops L. and Triticum L. Species exist in a polyploid series, diploid, tetraploid and hexaploid, based on the genome formula, n = x = 7 chromosomes. Commercial durum wheat is tetraploid with the genome formula BBAA, while bread wheat is hexaploid (BBAADD). Wheats grown at Riverside, California, from June to October exhibit heat stress at the vegetative and reproductive stages. Under high temperatures (28/15�C day/night) during the vegetative stage, many diploid species do not grow well. Wild diploid T. urartu (AA) and T. monococcum ssp. boeoticum (AA) exhibited more effects of heat stress than the goat grasses A. speltoides (SS = BB?) or A. tauschii (DD). Wild tetraploid T. turgidum L. ssp. dicoccoides Korn (BBAA) exhibited more vegetative-phase stress tolerance than the diploid wheats. Modern Mexican cultivars of durum and bread wheats showed good establishment under high field temperatures, but often tiller number was reduced, and the developmental stages were reduced in time. All the spring durum and bread wheats tested flowered and set seed. They produced anthers with fertile pollen, and they had reproductive heat tolerance. Many wild Aegilops and Triticum accessions did not boot for lack of vernalisation, or they showed reproductive heat stress. Ten wild accessions, including A. speltoides, A. longissima and A. searsii, showed normal vegetative and reproductive development and were considered heat tolerant. They came from the same geographic area in Palestine which should be searched for landraces of wheats that show heat tolerance.