QTL analysis of quantitative resistance to Phytophthora infestans (late blight) in tomato and comparisons with potato.

Quantitative trait loci (QTLs) for resistance to Phytophthora infestans (late blight) were mapped in tomato. Reciprocal backcross populations derived from cultivated Lycopersicon esculentum x wild Lycopersicon hirsutum (BC-E, backcross to L. esculentum; BC-H, backcross to L. hirsutum) were phenotyped in three types of replicated disease assays (detached-leaflet, whole-plant, and field). Linkage maps were constructed for each BC population with RFLPs. Resistance QTLs were identified on all 12 tomato chromosomes using composite interval mapping. Six QTLs in BC-E (lb1a, lb2a, lb3, lb4, lb5b, and lb11b) and two QTLs in BC-H (lb5ab and lb6ab) were most consistently detected in replicated experiments or across assay methods. Lycopersicon hirsutum alleles conferred resistance at all QTLs except lb2a. Resistance QTLs coincided with QTLs for inoculum droplet dispersal on leaves, a trait in L. hirsutum that may contribute to resistance, and dispersal was mainly associated with leaf resistance. Some P. infestans resistance QTLs detected in tomato coincided with chromosomal locations of previously mapped R genes and QTLs for resistance to P. infestans in potato, suggesting functional conservation of resistance within the Solanaceae.     

Effects of gymnemic acid on sweet taste perception in primates

Application of gymnemic acid (GA) on the tongue depresses thetaste of sucrose in man. This effect, as indicated by electrophysiologicalresponses, has been found to be absent in three nonhuman primatespecies. In the present behavioral study the effect of GA ontaste responses in 22 primate species, with two subspecies,and 12 human subjects has been investigated. In all the nonhumanprimates studied, including the Pongidae which are closely relatedto man, GA did not suppress the response to sucrose, only inman did GA have a depressing effect.     

Decomposition in situ of the sublittoral Antarctic macroalgaDesmarestia anceps Montagne

 Large amounts of detached Antarctic macroalgae accumulate in hollows of the seabed, where decomposition rates of the detached macroalgae are expected to be low, caused by lack of contact of the major part of the macroalgae with the sediment. To determine decomposition rates in Antarctic waters, untreated and pre-killed Desmarestia anceps fronds contained in nylon net bags were studied for 10 months under natural conditions in Factory Cove, Signy Island. Physical decomposition was shown to be more important than microbial decomposition. A weight loss of 40% occurred in untreated material within 313 days, while pre-killed material almost all disappeared within 90 days. Despite the weight loss, changes in chlorophyll a content were negligible during the experiment. Changes in the C:N ratio and tissue N indicated low rates of microbial decomposition. Therefore, it was concluded that weight loss was mainly caused by fragmentation, and particles disappearing from the nets accounted for most of the loss of original tissue. It remains unknown as to how long nutrients stay in Antarctic macroalgal litter before they become available to the system. Received: 16 March 1995/Accepted: 18 June 1995     

Seasonal waves of asthma: A possible botanical cause

The seasonal incidence of asthma and of shoot-growth in eucalypts in four Australian capital cities (Brisbane, Sydney, Adelaide and Melbourne) are compared. The incidence of asthma appears to be closely correlated with the initial stages of the seasonal flushes in shoot-growth of eucalypts, when rapid cell-division occurs. A spring to early summer growth flush invariably occurs in all capitals when the mean monthly temperature rises above 16–18°C; it is initiated progressively later with increasing latitude firstly in Brisbane, then in Sydney, then Adelaide and finally Melbourne. Although the correlation between asthma and eucalypt shoot-growth is high, there is not necessarily a cause-and-effect relationship. Volatile compounds evaporated from young and old leaves are probably not responsible, but the fine faecal pellets from the numerous small larvae and adult insects which attack the young eucalypt shoots may produce possible asthma-allergens. The concentration of these allergens in the atmosphere is reduced by heavy rainfall and by off-shore winds, and may accumulate during periods when temperature inversions occur at low levels in the atmosphere (e.g. during autumn in Brisbane).Supported by a grant from the Asthma Foundation of Queensland.     

The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus

Recombinant DNA clones have been isolated that contain 80 kb of the beta-globin complex from the deer mouse, Peromyscus maniculatus. Comparisons of this complex with that from the laboratory mouse, Mus domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3, Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin complex since the two species diverged. Unlike other mammals studied thus far, the deer mouse possesses three adult genes. Partial sequence analysis indicates that each of the three adult genes is intact and hence may be functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to genomic blots from Peromyscus reveals that it has a homologous counterpart in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO and Hbb-bhl, are also found in Peromyscus. The strong hybridization between the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO genes suggest that both pairs are important for the ontogeny of these mice although no known product has been identified for the Hbb-bhO genes. The presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication that created this related gene set occurred before the two lineages diverged. A single gene for Hbb-y has been isolated from Peromyscus. The adult region in Peromyscus has undergone significant divergence from the same region in Mus, having three rather than two adult genes, the acquisition of at least 15 kb of extra DNA relative to Mus, and possibly the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in contrast, contains the same set of genes apparently distributed over the same amount of DNA as in the Mus beta- globin complex. This observation suggests that the embryonic region of the complex is more evolutionarily stable than the adult region.      

Unusual cytological patterns in microsporogenesis in a cultivar of Fuchsia

Summary Multiple and multipolar spindles are a generalized feature of microsporogenesis in a cultivar of Fuchsia. Only the first meiotic division occurs and gives rise to sporads with nine microspores. Variation in chromosomal complements of the microspores is illustrated by pollen polymorphism. Since some of these pollen grains are able to germinate, the possible breeding value of this super-reductional type of division is questionable. Hypotheses concerning this phenomenon found in the literature are discussed in the light of our results.