Agronomic and economic assessment of intensive pest management of dry bean (Phaseolus vulgaris)

Two common production constraints of dry bean (Phaseolus vulgaris) in Ontario are annual weeds and anthracnose (caused by Colletotrichum lindemuthianum). Dry bean is not considered a competitive crop and weed interference can result in substantial yield losses, while anthracnose is considered one of the most devastating diseases in dry bean production. A study conducted in Ontario Canada, examined the effect of two herbicide programs on weed management, thiamethoxam insecticide treatment on plant enhancement and three fungicide programs on anthracnose development in a navy bean cv. ‘OAC Rex’. The premium herbicide program (s-metolachlor + imazethapyr) reduced percent weed ground cover relative to the economic herbicide program (trifluralin) in five of six locations. Thiamethoxam increased emergence and vigour at only one location, which contradicts reported benefits of thiamethoxam on plant health. The herbicide or thiamethoxam treatments did not affect anthracnose disease severity, visible seed quality, net yield or economic return. The fungicide seed treatment was often superior to the untreated control, for a number of the parameters measured. The application date of the foliar fungicide, relative to the onset of disease, varied between site-years. This dramatically influenced the fungicide’s effectiveness. Foliar fungicides increased seed quality and net economic return compared to the control when applied prior to disease development. The combination of fungicide seed treatment followed by a foliar fungicide provided the largest reduction in anthracnose severity.     

Genetics of intra-gene pool and inter-gene pool hybridization for seed traits in common bean (Phaseolus vulgaris L.) germplasm from Europe

Due to adaptation to new ecological and manmade conditions, the large diversity evolved in the European common bean germplasm is of particular interest for plant breeding. The knowledge of the genetic relationships within and among races and gene pools and their performance per se will provide bean breeders with a starting point in designing crosses using contrasting and complementary parents to broaden the genetic base within the different commercial classes. A genetic study of seed size variation and protein markers in progeny derived from 16 intraracial, interracial and inter-gene pools European common bean populations was conducted. General and specific combining ability (GCA and SCA) values were significant for seed weight, indicating that both additive and nonadditive genetic effects were involved in conditioning seed weight. Interracial populations showed transgressive values due to the accumulation of large-seeded alleles. Genetic variation inside Andean germplasm, and Chile and Peru races in particular, exhibited useful genetic progress in these populations, providing lines with a large seed size, and so, an excellent market potential. The distribution of incompatibility between both gene pools (Mesoamerican and Andean) of the common bean was explored. Inter-gene pool populations provided lower means of inbred segregants than the mid-parent value. Therefore, a good option it would be select for large seed size according to a recurrent or congruity inbred-backcrossing selection programs. Analysis of allele markers frequencies in inter-gene populations showed segregation distortion with a higher than expected frequency of alleles from the Mesoamerican gene pool, many of which were fixed in the F₇ lines. The presence of a great percentage of markers that showed segregation distortion in these populations (87%) indicated that this phenomenon can be amplified by using distance related common bean genotypes. In addition, a high percentage of heterozygotes for the Phs locus (for the seed storage protein phaseolin) was found, which suggest that the Andean homozygous TT could not be expressed in Mesoamerican genetic background due to the action of some form of female specific mechanisms that affected gene exchange between parental germplasm in inter-gene pool populations. The present work provides useful information in the establishment of large seed size germplasm that could have a great deal of interest among breeders and may offer some possibilities to exploit existing variation within and between common bean races.     

Agronomic performance of common bean (Phaseolus vulgaris L.) lines in an Oxisol

Soil acidity and low nitrogen (N) and phosphorus (P) availability are the most important constraints for common bean (Phaseolus vulgaris L.) production in highly weathered soils of the humid tropics. The objective of this study was to identify bean lines capable of producing higher yields as the result of greater N and P use efficiency under conditions of intermediate soil N and P availability. Selection for adaptation to low soil fertility can be used by plant breeding programs to improve bean seed yields. The performance of 33 bean lines and the varieties ‘Morales’ and ‘Verano’ from Puerto Rico and ‘Salagnac 90’ from Haiti were evaluated under three fertilization regimes in an Oxisol (very-fine, kaolinitic, isohyperthermic Typic Eutrustox): (i) 50 kg N/ha (+N), 57 kg P₂O₅/ha (+P), 54 kg K₂O/ha (+K), (ii) −N, +P and +K, and (iii) +N, −P and +K in two field plantings of June 2007 and January 2008. The black bean line PR0443-151 and red bean line PR0340-3-31 had consistently higher seed yields under nutrient non-limiting conditions (+N +P +K). The low N tolerant lines and those that consistently had the highest N use efficiencies were PR0443-151, VAX 3, RBF 11-33 and RBF 19-63. Lines that were both efficient in N utilization and responsive to N application were PR0443-151, IBC 309-23, and A774. PR0340-3-31, PR0443-151, A774 and VAX 3 had the highest seed yields under soil P limiting conditions and expressed high soil P use efficiency. The identification of the bean lines with high relative yields under both nutrient limiting and non-limiting conditions, high nutrient use efficiency, and tolerance to low soil N and P, can help breeding programs and eventual sustainability of bean production in the Caribbean.     

Effects of soaking,cooking and fermentation on composition,in-vitro starch digestibility and nutritive value of common beans

A common bean variety, grown in Burundi, was either fermented, soaked and/or cooked, and then assessed for nutrient composition, in-vitro starch digestibility and protein nutritive value. A decrease in ash, most minerals, vitamins, and some essential amino acids was noted for soaked, cooked and soaked-cooked beans. Compared to untreated beans, soaking decreased soluble sugar (9.8 percent) but increased starch (7.3 percent) and soluble fiber (16.9 percent). In cooked beans, an increase in soluble sugar (1.5 percent), and a decrease in thiamine (81.7 percent), starch (24.6 percent) and soluble fiber (16.6 percent) and nitrogen (2.9 percent) contents were observed. Crude fiber (6.9 percent) and starch (10.0 percent) increased while fat (17.6 percent), fatty acids (linoleic: 10.7 percent; linolenic: 14.3 percent) and soluble sugars (25.4 percent) and nitrogen (14.4 percent) decreased in soaked-cooked beans. Fermentation increased potassium (11.6 percent), soluble fiber (18.9 percent), and some amino acids but decreased fatty acids (linoleic: 13.5 percent; linolenic: 19.9 percent), soluble sugar (75.2 percent) and vitamin (riboflavin: 41.0 percent; niacin: 24.5 percent) contents in common beans. However, the in-vitro starch digestibility was greatly improved (12.3 percent) by cooking while it decreased in soaked beans (29.2 percent). Soaking-cooking and fermentation did not have any significant effect on the digestibility of common bean starch. Finally, among the five treatments applied to common beans, only fermentation showed a significant improvement (8.3 percent) on the protein nutritive value of this legume.     

Analysis of starch swelling power in Australian breeding lines of hexaploid wheat (Triticum aestivum L.)

Starch is the major component of wheat (Triticum aestivum L.) grain and is composed of two large glucan molecules, amylose and amylopectin. The ratio between the two polymers types influences the water absorbing properties of starch upon heating, and thus affects the end-use of grain and purified starch. In this study, we evaluated the starch swelling power (SSP) values in seven wheat populations developed from crosses involving low-SSP lines. Analysis of starch produced by the F₂ generation plants showed that the largest SSP variation (11.4–16.2) and lowest SSP mean (13.9) was obtained for a population derived from doubled haploid lines SM1028 (SSP = 14.5) and VK306 (SSP = 13.6). The population of 360 lines was advanced by single seed descent to the following generations for further studies. Starch analysis of grain produced by F₄ generation lines in two field locations during 2006 and in a greenhouse environment during 2005 showed that SSP values were relatively stably inherited. The average broad-sense heritability was 73% and significant (P < 0.001) genotype × genotype and genotype × environment interactions were seen. Starches with the highest and lowest SSP values were inversely related to amylose concentration determined by high pressure liquid chromatography (HPLC)–size exclusion chromatography (SEC) of debranched starch. Developed lines with the lowest SSP values surpassed 40% in apparent amylose concentration. The study illustrates that screening for SSP in early generations can be used to develop wheat lines with desired starch swelling characteristics.     

Effect of imazamox plus bentazon on dry bean (Phaseolus vulgaris L.)

Imazamox plus bentazon has the potential to provide broad spectrum weed control in dry bean (Phaseolus vulgaris L.). Field trials were conducted in Ontario over a two year period (2003 and 2006) to evaluate the effect of imazamox plus bentazon applied post-emergence at 25 + 600 and 50 + 1200 g ai ha⁻¹ on black, brown, cranberry, kidney, otebo, pinto, white and yellow eye beans. Treatments included a non-treated check. All treatments were maintained weed free during the growing season. The eight market classes responded similarly to imazamox plus bentazon. Imazamox plus bentazon applied post-emergence caused less than 4% visible injury at 7, 14 and 28 days after treatment. Imazamox plus bentazon applied post-emergence did not have any effect on plant height, shoot dry weight, seed moisture content and yield of dry bean. Based on these results, imazamox plus bentazon at the proposed maximum use dose can be safely used for weed management in black, brown, cranberry, kidney, otebo, pinto, white and yellow eye bean production in Ontario. Additional research is needed to determine if cultivars within a market class of dry bean differ in their response to imazamox plus bentazon.     

Water uptake during cooking of dry beans (Phaseolus vulgaris L.)

Water uptake during cooking of ten dry bean (Phaseolus vulgaris L.) varieties was investigated. Water uptake during early stages of cooking was characteristic of the variety. Although the optimal cooking times varied widely (52–85 min), all the beans absorbed similar amounts of water when cooked for their optimal times. Cooking times were significantly correlated with W_{20 min} (r=–0.92) and hardness index (r=0.76) of beans. Most other physical characteristics excepting the surface area of beans were generally unrelated to theW _{20 min},W _opt, and cooking times. No significant correlation was observed between phytate content and cooking times of beans. On cooking for their respective optimal times, all varieties absorbed nearly 1.5 times their weight of water and attained a moisture content of about 65% (wet basis).     

Identification of a GDSL-motif carboxylester hydrolase from rice bran (Oryza sativa L.)

A major esterase (designated OsEST1) showing high activity using 1-naphthyl acetate as a substrate was identified from rice bran and purified approximately 239-fold to near-homogeniety. The purified enzyme migrated as a single polypeptide band on native and SDS-polyacrylamide gels and had a molecular mass of 25 kDa under denaturing conditions. Analysis of its tryptic peptides by MALDI-TOF-MS and subsequent data mining identified a corresponding cDNA OsEST1 consisting of 714 nucleotides and encoding a 238 amino acid protein. Analysis of its primary sequence indicated that OsEST1 is a GDSL-motif carboxylester hydrolase belonging to the SGNH protein subfamily in containing the putative catalytic triad of Ser¹¹, Asp¹⁸⁷, and His¹⁹⁰. OsEST1 showed the highest catalytic activity at approximately pH 8.0–8.5 and at 45 °C with K_m and V_max values for 1-naphthyl acetate of 172 μM and 63.7 μmol/min/mg protein, respectively. However, OsEST1 showed no activity with triacylglycerol. Alignment of the primary sequence of OsEST1 and other rice GDSL-motif esterases/lipases showed that OsEST1 aligns with a specific family of plant SGNH esterases involved in response to dehydration and cuticle formation. These results suggest that OsEST1 is not a lipase but an esterase activity which has some other function in rice, especially during seed development.     

Variability in essential oil content and composition of Origanum hirtum L., Origanum onites L., Coridothymus capitatus (L.) and Satureja thymbra L. populations from the Greek island Ikaria

Plants belonging to four “oregano” plant species (Origanum hirtum L., Origanum onites L., Coridothymus capitatus L., and Satureja thymbra L.) were collected during flowering from 33 sites located in the eastern part of the Greek island of Ikaria in the Eastern Aegean during April, May and July 2008. C. capitatus and O. hirtum were mostly observed in higher altitudes, whereas O. onites and S. thymbra in lower ones. The spatial distribution of all species was depicted on a GIS map. All four species exhibited essential oil concentrations higher than those reported in earlier literature, namely O. onites 3-4.3%, S. thymbra 4-6.5%, C. capitatus 3.7-5.6% and O. hirtum 5.5-10.0% (v/w). Carvacrol was the main constituent of the essential oils of all species, followed by γ-terpinene, p-cymene and caryophyllene, while thymol was not detected. All constituents varied remarkably among the four species, with carvacrol exhibiting the lowest variation. Carvacrol content varied between 72.3 and 89.2% in O. onites; 46.5 and 58.0% in S. thymbra; 82.9 and 90.9% in C. capitatus; and 84.4 and 93.8% in O. hirtum. By applying hierarchical cluster analysis on the basis of the essential oil constituents two main groups, divided into four subgroups of the taxa were evident. The first group consisted of O. onites and S. thymbra, while the second one of C. capitatus and O. hirtum. The results are discussed in terms of topography and climatic variation.     

Development of simple and co-dominant PCR markers to genotype puroindoline a and b alleles for grain hardness in bread wheat (Triticum aestivum L.)

Grain hardness is one of the most important quality characteristics of cultivated bread wheat (Triticum aestivum L.). A large deletion in the puroindoline a (Pina) gene or single nucleotide polymorphisms (SNPs) in the puroindoline b (Pinb) gene results in hard grain texture. So far, nine Pina alleles (Pina-D1a–Pina-D1b, Pina-D1k–Pina-D1q) and seventeen Pinb alleles (Pinb-D1a–Pinb-D1g, Pinb-D1p–Pinb-D1ab) have been identified in bread wheat. The major Pina and Pinb alleles identified in hard wheat cultivars are Pina-D1b, Pinb-D1b, Pinb-D1c and Pinb-D1d. In this study, a three-primer PCR system was employed to develop nine co-dominant STS markers for genotyping Pina-D1a and Pina-D1b, whereas temperature-switch (TS) PCR was used to develop six co-dominant SNP markers for genotyping the Pinb-D1a, Pinb-D1b, Pinb-D1c and Pinb-D1d alleles. These STS and TS-PCR markers were used to verify the grain hardness genotype of 100 wheat cultivars. The reliability and genotyping accuracy of TS-PCR markers were confirmed through sequencing of PCR products and a comparison with previously published results. Therefore, STS and TS-PCR markers offer a simple, cost-effective and reliable method for high-throughput genotyping Pina and Pinb alleles to select grain hardness in wheat quality breeding programs and for wheat market classification.     

Differences in leaf yield and indigo precursors production in woad (Isatis tinctoria L.) and Chinese woad (Isatis indigotica Fort.) genotypes

Isatis tinctoria L. (woad) is one of the earliest known sources of indigo in Europe where it was cultivated since the Middle Ages. Isatisindigotica Fort. (Chinese woad), widely distributed in China, had been used from ancient times as indigo-producing plant and medicinal plant. Both species produce indigo precursors indican (indoxyl β-d glucoside) and isatan B (indoxyl ketogluconate) in their leaves. In order to identify new suitable crops for indigo production in Italy, 17 woad lines were studied under field conditions in Central Italy (Pisa, 43°40′N, 10°19′E) from 2001 to 2003. We analyzed the effects of year, genotype, and harvest times together with their reciprocal interactions on leaf yield and indigo precursors production. Woad lines were then compared with seven I. indigotica lines in a field crop experiment set up in 2003. Extraction and quantification of indigo precursors were accomplished by HPLC-ELSD. Isatan B and indican content, as well as equivalent indigo and fresh/dry leaf yield, were compared between species and among genotypes.     

Comparative susceptibility of Ostrinia furnacalis, Ostrinia nubilalis and Diatraea saccharalis (Lepidoptera: Crambidae) to Bacillus thuringiensis Cry1 toxins

Transgenic corn hybrids that express toxins from Bacillus thuringiensis (Bt) are highly effective against the European corn borer, Ostrinia nubilalis (Hübner), and the closely related Asian corn borer, Ostrinia furnacalis (Guenée). Since the registration of Bt corn hybrids in the U.S. in 1996, there has been a great deal of information generated on O. nubilalis. However, relatively little information exists for O. furnacalis. To help determine whether the information generated for O. nubilalis can be leveraged for decisions regarding the use of transgenic Bt corn against O. furnacalis, experiments were designed to determine whether the pattern of sensitivity to various Bt Cry1 toxins is similar between the two species. Test insects included laboratory-reared O. furnacalis originating from Malaysia, a Bt-susceptible laboratory colony of O. nubilalis maintained at the University of Nebraska-Lincoln (UNL) and an out-group consisting of the sugarcane borer, Diatraea saccharalis (F.), from Louisiana which represents a different genus from the same family. O. furnacalis and O. nubilalis exhibited a similar pattern of susceptibility to all the Cry1 toxins and were highly susceptible to the range of Bt toxins tested including Cry1Aa, Cry1Ab, Cry1Ac and Cry1F. Both of the Ostrinia species were more tolerant to Cry1Ba compared with D. saccharalis, although sensitivity of O. furnacalis was intermediate and did not differ significantly from that of O. nubilalis and D. saccharalis. D. saccharalis was also susceptible to the range of toxins tested but unlike the two Ostrinia species, was more tolerant to Cry1F and more susceptible to Cry1Ba. These results indicate that both of the Ostrinia corn borer species are similar in sensitivity to the Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1F toxins, thus suggesting shared toxin receptors and mechanisms of toxicity for the two species.     

Partial purification and characterization of polyphenoloxidase from durum wheat (Triticum durum L.)

A bright yellow color of pasta is an important qualitative trait for the durum wheat industry. Final color is the result of the balance between yellow and brown components in semolina. Polyphenoloxidase (PPO) is implicated as playing a significant role in darkening. This study aimed to characterize PPO activity of durum wheats. PPO was extracted and partially purified by ion-exchange chromatography on a column packed with diethyaminoethyl cellulose (DEAE). This procedure led to 26.33-fold purification with 24.7% recovery. The optimum temperature and pH of PPO were found to be 40 °C and 6.5, respectively. Heat stability of durum wheat PPO decreased as the temperatures increased from 30 to 80 °C. The z-value was calculated as 23.4 °C. It increased to 26.3 and 48.4 °C in the presence of 40% sucrose and 1 M NaCl, respectively. Durum wheat PPO was shown to use several phenolic compounds as substrate. Among the substrates used, the greatest substrate specificity was observed with catechol. Durum wheat PPO was sensitive to inhibitors such as ascorbic acid, cysteine, oxalic acid and citric acid. Ascorbic acid was the most effective inhibitor.     

Differential expression of defence-related proteins in Vigna unguiculata (L. Walp.) seedlings after infection with Fusarium oxysporum

This work aimed to study the induction of defence proteins in cowpea seedlings during the first days after infection with the fungi Fusarium oxysporum f. sp. cubenses and F. oxysporum f. sp. phaseoli. Cowpea seeds, after disinfection, were transferred to Petri dishes containing 0.5% agar and, after germination, were infected with a drop of a suspension containing 0.5 × 10⁴ spores ml⁻¹. Seedlings were collected at 24, 48, 72 and 96 h after infection and were dissected into leaves, hypocotyls, roots, cotyledons and teguments, which were measured and weighed for morphometric analysis. The agar medium was also analyzed. Enzymatic assays of proteic extracts yielded antimicrobial peptides detected by Western blotting. The cowpea seedlings showed a complex pattern of induction and repression of defence proteins in response to infection by both pathogens. Furthermore, morphometric analysis showed differences between infected and control seedlings. Infected samples did not at any time exhibit chitinase activity, but did exhibit different β-1,3-glucanase and peroxidase activities. Western blotting for lipid transfer protein (LTP) demonstrated its presence in all parts of the infected seedlings. Exuded proteins, also obtained from cowpea seeds in the germination medium, were separated by SDS-PAGE and tricine gel electrophoresis. The analysis showed that some proteins were exuded from moistened cowpea seeds, particularly after F. oxysporum infection.     

Growth and centelloside production in hydroponically established medicinal plant-Centella asiatica (L.)

Conditions to cultivate medicinally important herb Centella asiatica in hydroponic system are reported here for the first time. Growth kinetics of hydroponically grown plants was monitored over a period of 70 days. The maximum growth and dry matter accumulation (156.3% increment over the initial inoculum weight) in the cultured plants occurred around 42nd day. High Performance Liquid Chromatography (HPLC) analysis of the bioactive centellosides in the crude triterpenoids extract of the harvested leaves showed the presence of 11 mg, 1.7 mg, 36.6 mg and 6.3 mg of madecassoside, asiaticoside, madecassic acid and asiatic acid on per gram dry weight basis, respectively. The results of this study suggest that the cultivation of C. asiatica in hydroponic systems can be an effective platform for the production of clean and good quality C. asiatica herb for the pharmaceutical companies.     

Preparation and antinutritional characteristics of dry bean (Phaseolus vulgaris L.) protein concentrates

Protein concentrates and starches were prepared by a wet extraction process from five dry bean (Phaseolus vulgaris L.) cultivars. The protein contents ranged from 69.7–76.4%. Concentrates prepared from dehulled beans under similar conditions had higher protein contents (80.6–87.9%). Each additional washing of the concentrates with distilled water increased their protein content. However, the protein recovery progressively decreased. The yield of starch ranged from 48.0–51.1% of the starting material. The solubility of bean proteins was minimal at pH 4.0, and under alkaline conditions, it was influenced by the tannin contents of the concentrates. Protein concentrates had lower trypsin, chymotrypsin, and amylase inhibitory activities as well as lower phytic acid and tannin contents compared to whole bean flours.     

Screening of three sweet potato (Ipomoea batatas L.) cultivars for resistance to different virulence groups of root-knot nematodes (Meloidogyne spp.) under controlled conditions

The susceptibility of three sweet potato cultivars (Ipomoea batatas L.) C4, TIS 3290 and TIS 9162 was evaluated against 156 isolates of Meloidogyne spp. with the aim to include resistant/tolerant sweet potato cultivars in a crop rotation scheme for the management of root-knot nematodes. The nematode isolates corresponded to races 1, 2 and 3 of Meloidogyne arenaria (n = 7), races 1, 2, 3 and 4 of M. incognita (n = 131) and Meloidogyne javanica (n = 18). Also, the isolates of M. incognita were differentiated in virulence groups: Pepper (n = 35), Pepper-Mi (n = 25), Tomato (n = 41) and Tomato-Mi (n = 30), depending on their ability to parasitize resistant pepper and tomato cultivars. The tested isolates of M. javanica parasitized C4 and TIS 3290, but not TIS 9162, whereas M. arenaria parasitized C4 and TIS 9162, but not TIS 3290, and M. incognita was able to parasitize the three sweet potato cultivars tested. C4 was the most susceptible cultivar to all nematode species tested, especially M. incognita, TIS 3290 was the most resistant and TIS 9162 was in between (7.2, 62.9 and 26.9% of resistant plants, respectively). Susceptibility of the sweet potato cultivars showed slight variations depending on the race or virulence group of M. incognita. The results suggest that sweet potato cultivars TIS 3290 and TIS 9162 may be used as rotation crops in fields where root-knot nematodes are present, their selection depending on the Meloidogyne isolates present. The use of resistant sweet potato cultivars would be preferably combined with other management practices to avoid virulence selection in nematode isolates.     

High level of resistance to Sclerotinia sclerotiorum in introgression lines derived from hybridization between wild crucifers and the crop Brassica species B. napus and B. juncea

Sclerotinia rot caused by the fungus Sclerotinia sclerotiorum is one of the most serious and damaging diseases of oilseed rape and there is keen worldwide interest to identify Brassica genotypes with resistance to this pathogen. Complete resistance against this pathogen has not been reported in the field, with only partial resistance being observed in some Brassica genotypes. Introgression lines were developed following hybridization of three wild crucifers (viz. Erucastrum cardaminoides, Diplotaxis tenuisiliqua and E. abyssinicum) with B. napus or B. juncea. Their resistance responses were characterized by using a stem inoculation test. Seed of 54 lines of B. napus and B. juncea obtained from Australia, India and China through an Australian Centre for International Agricultural Research (ACIAR) collaboration programme were used as susceptible check comparisons. Introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum had much higher levels (P < 0.001) of resistance compared with the ACIAR germplasm. Median values of stem lesion length of introgression lines derived from the wild species were 1.2, 1.7 and 2.0 cm, respectively, as compared with the ACIAR germplasm where the median value for stem lesion length was 8.7 cm. This is the first report of high levels of resistance against S. sclerotiorum in introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum. The novel sources of resistance identified in this study are a highly valuable resource that can be used in oilseed Brassica breeding programmes to enhance resistance in future B. napus and B. juncea cultivars against Sclerotinia stem rot.     

The critical period for weed competition in French bean (Phaseolus vulgaris L.) in Mediterranean areas

Field experiments were carried out in 2004 and repeated in 2005 and 2006 in central Italy to determine the effect of competition from a natural weed flora on growth and yield of French bean (Phaseolus vulgaris L.). Two treatments were applied; weeds were either allowed to infest the crop or plots were kept weed free for an increasing duration of time (0, 7, 21, 28, 35, 45 days) after crop emergence. To assess the critical period of weed competition (CPWC) and the influence of weed infestation on yield, the Gompertz and logistic equations were fitted to data which represented the increasing duration of weed-free and weed-infested periods, respectively. During the three years of the experiment weeds, allowed to interfere for the whole growing season, reduced fresh pods yields up to 60%, 65% and 59% of the weed-free bean plots. Based upon an arbitrary yield loss (AYL) of 5%, the CPWC was from 50 Growing Degree Days (GDD) to 284 GDD, i.e. from 11 days after emergence (DAE) to 28 DAE. These values correspond to the lowest and highest values observed in the three experiments respectively for the weed-infested and weed-free period.     

Yield response of okra, Abelmoschus esculentus (L.) Moench to leaf damage by the flea beetle, Podagrica uniforma Jacoby (Coleoptera: Chrysomelidae)

Yield-related response of okra plants, Abelmoschus esculentus (L.) Moench, to artificial infestation of the flea beetle (Podagrica uniforma Jac.) at different densities (0, 5, 10, 20, 30, and 40 pairs per cage) was studied in screen house and field experiments. In both experiments, increase in beetle density resulted in a significant reduction (P < 0.05) in fruit production, fruit length, fruit width, fresh fruit weight, number of seeds per fruit, 100 seed weight and fresh fruit yield. In addition, higher densities caused more dry matter accumulation in the seeds than in the husk of okra fruits. Compensation was noticed at the 5- and 10-pair levels of infestation in some of the variables measured. Fresh fruit yield reduction was more than 50% when beetle density was increased beyond 20 pairs per cage in both experiments. The lowest density of P. uniforma at which significant reduction (P < 0.05) occurred in fresh fruit yield per cage, when compared with the control, was the 20-pair level, representing the damage threshold of the beetle at which initiation of control measures would be justified. Regression analysis indicated that flea beetle density was linearly associated with fruit damage and fresh fruit yield. Also, chi-square analysis showed that the models derived from the screen house and field experiments were not significantly different (P < 0.05) from each other, and either could be used for prediction purposes.