Use of culture-derived Fusarium oxysporum f. sp. cubense, race 1 filtrates for rapid and non-destructive in vitro differentiation between resistant and susceptible clones of field-grown banana

Banana and plantain are among the most important food crops in developing countries but production is threatened by increasing virulent forms of Fusarium oxysporum f. sp. cubense. Chemical control is not economically effective and,therefore, breeding programs are necessary. Traditional field studies of new genotype resistance to this disease are time-consuming and destructive. Therefore,we developed a rapid and non-destructive procedure to differentiate field-grown banana resistant from susceptible clones. This procedure implicates application of culture filtrates of Fusarium oxysporum f. sp. cubense race 1 onto banana leaves. The relationship between duration of the fungal in vitro incubation, and the fungal culture fresh mass, the culture filtrate absorbency, and the Gross Michel (susceptible cultivar)leaf lesion area (after application of the culture filtrate) were similar and at 24day-incubation the highest values of the recorded indicators were observed. A comparison between Gross Michel and FHIA-01(resistant) was also performed. The most relevant differences between cultivars were observed at 48 hours after application of the culture filtrate, and in the middle-aged leaves. The position of the culture filtrate application in the leaf limb (distal, middle, proximal) was not determinant. A wider comparison among banana cultivars confirmed previous results informed by other researchers using different systems to study this plant-fungus interaction. Such a confirmation validates the effectiveness of the procedure described here to select rapid and non-destructively banana resistance to this disease at field level. This revised version was published online in August 2006 with corrections to the Cover Date.     

Potential of a Fusarium eumartii culture filtrate on the screening for wilting resistance in potato

Summary Fusarium solani f.sp. eumartii Carp. Snyder and Hansen (Fusarium eumartii) is a soil inhabitant that induces the so-called Potato Wilt and Stem End Rot disease. Prior to wilting, the pathogen induces peculiar small bronze spots on the leaflets. Failure to isolate F. eumartii from infected leaflets suggests the involvement of a toxin in the disease. The fungus was grown in liquid Richard's medium and thereafter a filtrate was obtained dialyzing (MW cutoff 12,000–14,000) and sterilizing the culture by filtration (0.22 m). Potato leaves treated with both the pathogen or the filtrate showed symptoms of bronze spots and significantly higher electrolyte leakage when compared to controls. Tomato leaves showed neither bronze spots nor electrolyte leakage after plant inoculation with the pathogen or with the filtrate treatment. Both, the absence of visible symptoms and the lack of electrolyte leakage in tomato could be associated to a certain degree of host specificity of the F. eumartii filtrate towards potato. The filtrate also induced symptoms similar to infections by F. eumartii in adult plants and in vitro plantlets of cultivars Huinkul MAG and Kennebec. Callus responses to the filtrate were related to responses of the cultivars to the pathogen in greenhouse. These results show the potential of the culture filtrate of F. eumartii for use in screening for wilting resistance.     

Effect of incubation temperature regimes and culture medium on broccoli microspore culture embryogenesis

Conditions for reliable induction of embryogenesis from isolated microspores were studied in ten genotypes of broccoli. Embryo yields were significantly increased in almost all of the broccoli genotypes by the incubation at 32.5 ^°C for 1 day, than when the standard incubation at 30 ^°C for 2 days was used. Treatments of 48 hours at 32.5 ^°C produced less than optimal results suggesting that broccoli microspores are more sensitive to high temperatures than those of B. napus. The use of the ¹/₂ NLN-13 medium yielded greater number of embryos than the standard NLN-13. The magnitude of the response to the redution of the concentration of major salts by half in the NLN medium varied with the different genotypes. High embryogenic broccoli cultivars, such as ‘Shogun’, ‘SDB9’, and ‘Green Valiant’, presented a better response to the reduction of the concentration of major salts by half in NLN-13. Reduction never produced a detrimental effect on embryo yield and seems not to have any effect in the subsequent development of embryos in plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Precision of genetic relationship estimates based on molecular markers

Genetic progress through selection is directly related to the amount of variability present in the population and the quality of genes contributed by the parents. Genetic relationships between lines were studied using DNA marker-based estimates of genetic similarity. A statistical methodology using the width of a confidence interval was developed to determine the number of probes to be surveyed and the precision in the estimation of genetic distance between pairs of cultivars. Precision was affected by type of genetic distance used, the number of cultivars, and amount of genetic diversity present in the studied group. The width of a (1-α)% confidence interval decreased as the number of RFLP fragments increased. Oat and wheat diversity studies were used to illustrate the methodology. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of Aluminum Tolerance and its Effects on Grain Yield and Grain Quality in Oats (Avena Sativa L.)

Summary Aluminum toxicity due to the cation Al⁺³ is a major factor limiting yields in acid soils. Wide genetic variability to aluminum tolerance is found in oat genotypes. The objectives of this study were to determine the number of genes controlling aluminum tolerance in oats and to verify if any detrimental effects were present of the aluminum tolerance genes on grain yield and grain quality in Al⁺³free soils. Aluminum tolerance was estimated as the average regrowth of the main root after exposure to toxic levels of Al⁺³ in a hydroponic solution under controlled conditions. The number of genes controlling that trait was estimated from the distribution of the average root regrowth frequencies in a population of 333 recombinant inbred lines (RIL's) in generations F_5:6 and F_5:7. The effects on grain yield and grain quality were assessed in a subpopulation of 162 RIL's chosen based on their aluminum tolerance response. Aluminum tolerance in the evaluated population was controlled by one dominant major gene with the tolerant genotypes carying Al _a Al _a and the sensitive ones al _a al _a alleles. No detrimental effects of the Al _a allele on grain yield or grain quality were detected.Part of the Master of Science dissertation of the first author     

Selection for seed yield in Andean intra-gene pool and Andean × Middle American inter-gene pool populations of common bean

Yields of large-seeded Andean (A) common bean (Phaseolus vulgaris L.) cultivars of Chile and Nueva Granada races are 40 to 60% lower compared to their Middle American (M) counterparts of small-seeded Mesoamerica and medium-seeded Durango races. Our objective was to use the concept of congruity backcrossing between Andean x Middle American inter-gene pool [AM 11833 = A 483 (A)///// A 686 (M) //// PVA 800A(A)/// ‘Carioca’ (M)// Carioca (M)/ G 19833 (A)] and between races within Andean gene pool [i.e., intra-gene pool Andean, AA 11834 = A483 (A)//// ‘Cardinal’(A) /// ‘Blanco Español’(A) // BlancoEspañol (A) / ‘Taylor’ (A)] to compare selection for seed yield improvement of large-seeded Andean beans. Seven hundred sixty seven F₂-derived F₃ (F_2:3) families were produced for each population. Visual appraisal for total plant performance, combined with seed yield from non-replicated plots was used for selection of 551 families in F_2:3, 182 families in F_2:4, and 91 families in F_2:5 in each population. Eight hundred twenty three F_5:6 lines were developed from the 91 F_2:5 families in each population. Visual selection, combined with seed yield in non-replicated plots was again used to select 294 lines in F_5:6 in each population. Similarly, 44 highest yielding F_5:7 lines were selected in AM 11833 and 39 F_5:7 lines in AA 11834. Thus, single plant selections were made in the F₂ and F₅, and plants within each plot were harvested in bulk in F₃, F₄, F₆, and F₇. Thirty nine F_5:8 lines from AA 11834 and 44 lines from AM 11833, parents, and checks were evaluated at Popayán and Quilichao, Colombia in 1998 and 1999. Selected lines in both populations, on average, out-yielded the mean of their large-seeded Andean parents. Mean yield of the lines selected from AM 11833 was 50% higher than AA 11834 lines. Twelve F_5:8 lines out-yielded the highest yielding Andean parents G 19833 and A 483 in AM 11833, whereas only one line yielded significantly higher (p < 0.05) than the highest yielding parent A 483 in AA 11834. However, none of selected lines out-yielded small-seeded Middle American parents used in AM 11833 (A 686 and ‘Carioca’). The mean 100 seed-weight of AA 11834 was 36 g compared to 28 G for AM 11833 F_5:8 lines. Selected lines had similar days to maturity as parents in AM 11833, and matured 3 d later in AA11834. Correlation coefficients between yield and 100 seed-weight were negative in both populations. Yield and days to maturity were positively correlated in AA 11834.     

Inter-and intraracial hybridization and selection for seed yield in early generations of common bean,Phaseolus vulgaris L.

Summary Five parents from each of four race groups of common bean (Phaseolus vulgaris L.) were hybridized to produce five crosses within each group. Also, five crosses were made for each of the six possible combinations among four groups. Parents, F₁ and F₂, and parents, F₂ and F₃ were evaluated for seed yield in 1990 and 1991, respecitively, at two locations in Colombia.Yield of parents belonging to Middle American races and crosses among them was higher than that of races of Andean origin. Positive correlations were found among the mid-parent value, F₁, F₂ and F₃. Also, the mid-parent value predicted the mean seed yield of all possible lines that could be derived from the F-generation in 42 out of 47 crosses. Four crosses, all between common bean races of Andean and Middle American origin, indicated a possible loss of favorable epistatic parental alleles. On average, mean yield of interracial F₁ hybrids was higher than that of intraracial ones.Positive heteroris (26.4%–123.8%) over the mid-parent in 31 crosses, and F₁s yielding higher (23.7%–91.8%) than the high parent in 20 crosses and yielding higher (22.1%–53.2%) than the highest control among all parents (MAM 13) in 12 crosses, were found. Heritability, estimated by the parent-offspring regression, ranged from 0.42± 0.07 to 0.49±0.04. Expected and realized gains from selection (at 20% selection pressure) ranged from 10.3% to 21.0% over the mean of F₁ hybrids and F₂ and F₃ population bulks.     

Comparison of recurrent and congruity backcrossing for interracial hybridization in common bean

Summary Two common bean (Phaseolus vulgaris L.) cultivars were used for recurrent backcrossing (i.e., repeated backcrossing to one of the parents) to both parents independently and for congruity backcrossing (i.e., backcrossing alternately to both parents). One cultivar, ICA Pijao of race Mesoamerica, was late maturing, with erect type II growth habit and small seeds. The other was Pinto UI 114 of race Durango, an early maturing cultivar with prostrate type III growth habit and medium seeds. One to three recurrent backcrosses (RBC) to both parents, and two rounds of congruity backcrosses (CBC), were made. Thirty-two random lines from each method along with two parents were compared in a reps-in-set design at two locations (Popayán and Quilichao) in Colombia in 1992–1993.Differences between lines derived through different methods were found for seed yield, 100-seed weight, days to maturity, growth habit, and seed color pattern. The RBC to ICA Pijao produced lines with relatively higher seed yield, smaller seed size, and delayed maturity. Similarly, the RBC to Pinto UI 114 produced lines with reduced yield, medium seed size, and earlier maturity. All lines from one, two, and three RBC to Pinto UI 114 had type III growth habit. While most lines from the RBC to ICA Pijao had erect type II Growth habit, a few type III lines were also found in all the RBC. The lines derived from the CBC mostly possessed yield, maturity, and seed characteristics between those of the two parents and lines derived from RBC to both parents independently. They also had more variation for growth habit. To maximize recombination between and retention of desirable traits from distantly related parents used in interracial crosses, use of the CBC is suggested.     

Immigrants Doing Business in a Mid‐sized Canadian City: Challenges,Opportunities, and Local Strategies in Kelowna,British Columbia

Lacking a tradition of settling immigrants and the appropriate infrastructure to integrate them, small‐ and medium‐sized cities often face the challenge of attracting and retaining immigrants. Using a mixed methods approach, this study compares the experiences of immigrant and non‐immigrant entrepreneurs in a mid‐sized Canadian city, Kelowna, British Columbia. A survey reveals different experiences between these two groups, with immigrants facing more challenges. In the absence of institutionally complete communities or strong ethnic economies, immigrants do not rely extensively on their own community resources, an element considered instrumental for immigrant business development in large cities. Compared to non‐immigrants, immigrant entrepreneurs have a more optimistic outlook on doing business in Kelowna; this is encouraging for a city trying hard to attract immigrant investment. Key informants recommended transforming the city into a more welcoming community, establishing appropriate support infrastructure, and removing potential institutional offsets. This paper adds new theoretical insights to the literature on immigrant entrepreneurship; all socio‐cultural, political‐institutional, and economic‐structural considerations are embedded in geography. The findings also have implications for growth strategies in small‐ and medium‐sized cities.