Anthracnose In Common Bean Research Articles

Advancing common bean (Phaseolus vulgaris L.) disease detection with YOLO driven deep learning to enhance agricultural AI

Common beans (CB), a vital source for high protein content, plays a crucial role in ensuring both nutrition and economic stability in diverse communities, particularly in Africa and Latin America. However, CB cultivation poses a significant threat to diseases that can drastically reduce yield and quality. Detecting these diseases solely based on visual symptoms is challenging, due to the variability across different pathogens and similar symptoms caused by distinct pathogens, further complicating the detection process. Traditional methods relying solely on farmers’ ability to detect diseases is inadequate, and while engaging expert pathologists and advanced laboratories is necessary, it can also be resource intensive. To address this challenge, we present a AI-driven system for rapid and cost-effective CB disease detection, leveraging state-of-the-art deep learning and object detection technologies. We utilized an extensive image dataset collected from disease hotspots in Africa and Colombia, focusing on five major diseases: Angular Leaf Spot (ALS), Common Bacterial Blight (CBB), Common Bean Mosaic Virus (CBMV), Bean Rust, and Anthracnose, covering both leaf and pod samples in real-field settings. However, pod images are only available for Angular Leaf Spot disease. The study employed data augmentation techniques and annotation at both whole and micro levels for comprehensive analysis. To train the model, we utilized three advanced YOLO architectures: YOLOv7, YOLOv8, and YOLO-NAS. Particularly for whole leaf annotations, the YOLO-NAS model achieves the highest mAP value of up to 97.9% and a recall of 98.8%, indicating superior detection accuracy. In contrast, for whole pod disease detection, YOLOv7 and YOLOv8 outperformed YOLO-NAS, with mAP values exceeding 95% and 93% recall. However, micro annotation consistently yields lower performance than whole annotation across all disease classes and plant parts, as examined by all YOLO models, highlighting an unexpected discrepancy in detection accuracy. Furthermore, we successfully deployed YOLO-NAS annotation models into an Android app, validating their effectiveness on unseen data from disease hotspots with high classification accuracy (90%). This accomplishment showcases the integration of deep learning into our production pipeline, a process known as DLOps. This innovative approach significantly reduces diagnosis time, enabling farmers to take prompt management interventions. The potential benefits extend beyond rapid diagnosis serving as an early warning system to enhance common bean productivity and quality.

Mapping of adult plant recessive resistance to anthracnose in Indian common bean landrace Baspa/KRC 8.

The common bean (Phaseolus vulgaris) has become the food of choice owing to its wealthy nutritional profile, leading to a considerable increase in its cultivation worldwide. However, anthracnose has been a major impediment to production and productivity, as elite bean cultivars are vulnerable to this disease. To overcome barriers in crop production, scientists worldwide are working towards enhancing the genetic diversity of crops. One way to achieve this is by introducing novel genes from related crops, including landraces like KRC 8. This particular landrace, found in the North Western Himalayan region, has shown adult plant resistance against anthracnose and also possesses a recessive resistance gene. In this study, a population of 179 F2:9 RIL individuals (Jawala ×KRC 8) was evaluated at both phenotypic and genotypic levels using over 830 diverse molecular markers to map the resistance gene present in KRC 8. We have successfully mapped a resistance gene to chromosome Pv01 using four SSR markers, namely IAC 238, IAC 235, IAC 259, and BM 146. The marker IAC 238 is closely linked to the gene with a distance of 0.29cM, while the other markers flank the recessive resistance gene at 10.87cM (IAC 259), 17.80cM (BM 146), and 25.22cM (IAC 235). Previously, a single recessive anthracnose resistance gene (co-8) has been reported in the common bean accession AB 136. However, when we performed PCR amplification with our tightly linked marker IAC 238, we got different amplicons in AB 136 and KRC 8. Interestingly, the susceptible cultivar Jawala produced the same amplicon as AB 136. This observation indicated that the recessive gene present in KRC 8 is different from co-8. As the gene is located far away from the Co-1 locus, we suggest naming the recessive gene co-Indb/co-19. Fine mapping of co-Indb in KRC 8 may provide new insights into the cloning and characterization of this recessive gene so that it can be incorporated into future bean improvement programs. Further, the tightly linked marker IAC 238 can be utilized in marker assisted introgression in future bean breeding programs. The novel co-Indb gene present in Himalayan landrace KRC 8, showing adult plant resistance against common bean anthracnose, is independent from all the resistance genes previously located on chromosome Pv01.

Fine mapping of a new common bean anthracnose resistance gene (Co-18) to the proximal end of Pv10 in Indian landrace KRC-5.

Mapping and fine mapping of bean anthracnose resistance genes is a continuous process. We report fine mapping of anthracnose resistance gene Co-18 which is the first anthracnose gene mapped to Pv10. The discovery of resistance gene is a major gain in the bean anthracnose pathosystem research. Among the Indian common bean landraces, KRC-5 exhibit high levels of resistance to the bean anthracnose pathogen Colletotrichum lindemuthianum. To precisely map the anthracnose resistance gene, we used a Recombinant Inbred Line (F2:9 RIL) population (KRC-5 × Jawala). The inheritance test revealed that KRC-5 carries a dominant resistance gene temporarily designated as Co-18. We discovered two RAPD markers linked to Co-18 among 287 RAPD markers. These RAPD markers were eventually developed into SCARs (Sc-OPR15 and Sc-OPF6) and flank Co-18 on chromosome Pv10 at a distance of 5.3 and 4.2cM, respectively. At 4.0-4.1Mb on Pv10, we detected a SNP (single-nucleotide polymorphism) signal. We synthesized 58 SSRs and 83 InDels from a pool of 135 SSRs and 1134 InDels, respectively. Five SSRs, four InDels, and two SCARs were used to generate the high-density linkage map, which led to the identification of two SSRs (SSR24 and SSR36) that are tightly linked to Co-18. These two SSRs flank the Co-18 to 178kb genomic region with 13 candidate genes including five NLR (nucleotide-binding and leucine-rich repeat) genes. The closely linked markers SSR24 and SSR36 will be used in cloning and pyramiding of the Co-18 gene with other R genes to develop durable resistant bean varieties.

Antifungal activity of Origanum vulgare and Rosmarinus officinalis phenolics-containing extracts against Colletotrichum lindemuthianum and in the suppression of anthracnose in common beans

Oregano (Origanum vulgaris L.) and rosemary (Rosmarinus officinalis L.) may contribute to the control of anthracnose in common bean (Phaseolus vulgaris L.). This study aimed to investigate the chemical composition of both extracts by LC-HRMS and their in vitro and in vivo inhibitory activity against C. lindemuthianum isolates. We evaluated the inhibition of mycelial growth, the inhibition of the conidia germination, the phytotoxicity of the extracts in bean detached leaves and the reduction of severity of anthracnose under greenhouse conditions. Ten phenolics were identified: caffeic, p-coumaric, ferulic, gallic, gentisic, protocatechuic and vanillic acids, and quercetin, luteolin and naringenin. Gentisic acid was not reported for these plants in the consulted literature. We verified the complete inhibition of the mycelium growth of C. lindemuthianum by both extracts at about 2% (oregano) and 3% (rosemary), the inhibition of spore germination was for rosemary: 100% and for oregano: 85%, at a concentration of 3% of extracts and no symptoms of phytotoxicity were observed in common bean leaves treated with them. Both extracts were efficient in reducing the severity of anthracnose caused by C. lindemuthianum BRM 007447 in BRS Campeiro and Perola cultivars, in preventive and curative modes. These extracts have shown promise in the practice of sustainable agriculture, under the experimental conditions used.

Potential parents of carioca bean for use in breeding aiming resistance to Colletotrichum lindemuthianum

AbstractCarioca common bean (Phaseolus vulgaris L.) is the most produced and consumed in Brazil. The production of carioca bean is affected by fungal diseases such as anthracnose, caused by the fungus Colletotrichum lindemuthianum. Most sources resistant to anthracnose, used in crosses by breeding programs are not derived from the commercial group or are poorly productive and less adapted. Thus, the objective of this study was to characterize 40 carioca bean cultivars already recommended in Brazil for their reaction to C. lindemuthianum races 65, 73, 81, and 89. The cultivars and the resistant control, BRS Esplendor, were inoculated in a greenhouse with two different experiments for each race. Seedlings with fully expanded primary leaves were inoculated with a suspension of each pathogen race and assessed after 12 d. Among the 40 cultivars assessed, 12.5, 2.5, 12.5, and 15% resistant to one, two, three, and four races of C. lindemuthianum, respectively. The cultivars IAC Formoso, IAC‐Carioca Pyatã, IAC‐Apuã, VC 15, BRS Notável, and IPR Campos Gerais were resistant to the four races, constituting parental sources of resistance to the pathogen. In regions that favor the occurrence of anthracnose in common bean, cultivars with certain levels of resistance should be selected. Therefore, the important information obtained will be made available to growers and those offering technical assistance to growers.

Introgression of anthracnose resistance gene(s) into common bean (Phaseolus vulgaris)

Abstract. Kazimoto GK, Nchimbi-Msolla SF, Mabagala RB. 2022. Introgression of anthracnose resistance gene(s) into common bean (Phaseolus vulgaris). Cell Biol Dev 6: 20-31. Common bean anthracnose disease caused by the fungus Colletotrichum lindemuthianum causes significant yield losses. It is most destructive in areas with cool temperatures and high humidity (90-100%). The study aimed to introduce resistance genes into adapted but susceptible local cultivars of Masai Red and Soya Njano using conventional breeding methods. Five races of C. lindemuthianum were isolated and named from thirty-two common bean-diseased plant samples collected from Northern Tanzania. The sources of resistant genes were bean cultivars G2333 and AB136. Early developed populations were evaluated under field conditions in high altitude and humid environments at Bashnet in the Manyara region, in the Northern highlands of Tanzania. Both F2 and F3 populations of Soya Njano x G2333 were segregated for C. lindemuthianum resistance at a 9:7 ratio. Such segregation implied that two dominant epistatic genes conferred from G2333, the resistance being in the mode of epistatic gene interaction. The crosses between Masai Red x G2333 and F2 and F3 populations segregation ratio was 10:6, implying two dominant resistant genes were transferred to developed populations. The F2 and F3 progenies obtained from crossing Soya Njano and AB136 showed a ratio of 3:1. The F2 progenies from a cross between Masai Red and AB136 were segregated at a ratio of 3:1 and F3 progenies were 3:1. The 3:1 ratio confirmed single dominant gene inheritance conferred to developed progenies. The heritability (h²) from populations of Soya Njano x G2333 and Masai Red x G2333 was between 0.41 and 0.45. While Soya Njano, Masai Red, and A136 were between 0.2 and 0.53, which implied moderate heritability. F2 and F3 populations developed need further testing using MAS to confirm the presence of resistant genes. Multi-location testing should be done to verify the resistance levels of the developed bean population in later generations.

Molecular characterization of parental lines and validation of SNP markers for anthracnose and angular leaf spot in common bean

Molecular characterization of parental lines and validation of SNP markers for anthracnose and angular leaf spot in common bean

The current status, farmers’ management practices, knowledge, and perceptions of common bean anthracnose in Tanzania

The current status, farmers’ management practices, knowledge, and perceptions of common bean anthracnose in Tanzania

Bioefficacy and phytotoxicity of coordinated fungicide (fluopyram 200 + tebuconazole 200-400 SC) against anthracnose and angular leaf spot disease of common bean under wet temperate conditions of Himachal Pradesh

Bioefficacy and phytotoxicity of coordinated fungicide (fluopyram 200 + tebuconazole 200-400 SC) against anthracnose and angular leaf spot disease of common bean under wet temperate conditions of Himachal Pradesh

Characterization of Colletotrichum lindemuthianum Races in Zambia and Evaluation of the CIAT Phaseolus Core Collection for Resistance to Anthracnose.

Colletotrichum lindemuthianum, the causal pathogen of common bean (Phaseolus vulgaris) anthracnose, is highly variable. Therefore, understanding its race structure and identification of new sources of resistance is necessary for the development of varieties with durable resistance. The objectives of this study were (i) to characterize isolates of C. lindemuthianum collected from three major bean-growing regions in Zambia and (ii) evaluate the International Center for Tropical Agriculture (CIAT) Phaseolus core collection for resistance to C. lindemuthianum races 37, 73, and 566 and a blend of 20 races. Isolates collected from three major bean-growing districts in Zambia, namely Mporokoso, Mpika, and Mbala, were characterized as races 37, 73, and 566, respectively. A subset of the CIAT core collection comprising 885 accessions of common bean, 13 accessions of scarlet runner bean (Phaseolus coccineus), and 11 accessions of year bean (Phaseolus dumosus) was evaluated for resistance to races 37, 73, and 566 and a blend of 20 races in a greenhouse at the University of Zambia, Lusaka, Zambia. Totals of 72, 66, 48, and 9% of P. vulgaris accessions evaluated were highly resistant to races 37, 73, and 566 and a blend of 20 races, respectively. Also, accessions of P. coccineus and P. dumosus highly resistant to races 37, 73, and 566 were identified. Only eight of the 331 P. vulgaris accessions were highly resistant to all three individual races (37, 73, and 566) and to a blend of 20 races. These eight accessions constitute a valuable breeding resource for developing varieties with durable resistance to C. lindemuthianum.

Heterothallism among spatiotemporally diverse Colletotrichum lindemuthianum isolates and its implication in common bean anthracnose resistance breeding in the Northwestern Himalayan region

Heterothallism among spatiotemporally diverse Colletotrichum lindemuthianum isolates and its implication in common bean anthracnose resistance breeding in the Northwestern Himalayan region

English

Common bean anthracnose caused by Colletotrichum lindemuthianum is one of the major biotic constraints to production of French beans (Phaseolus vulgaris L.) in Kenya. This study aimed at screening French bean genotypes in relation to their response to common bean anthracnose in order to identify potential sources of germplasm for breeding. The genotypes were tested in three sites (Kakamega, Mwea and Kutus) where results revealed a significant genotype by environment interaction effect (p ≤ 0.05) which emphasizes the strong influence of the growing conditions on the expression of host resistance. Physiological characterization identified a total of 14 distinct races out of 16 successfully plated isolates, revealing a very high diversity of C. lindemuthianum in Kenya. Six races have not been reported in previous studies in the country and are considered as new races, that is, races 84, 141, 246, 515, 576 and 768. Andean race 401 was the most virulent race with a virulence index of 67% among the genotypes. Molecular analysis using six sequence characterized amplified region (SCAR) markers revealed polymorphism among the genotypes. The SCAR markers SBB-14, SH-18 and SAB-03 have shown to be useful for marker assisted selection (MAS) of the target resistance genes. This study has also identified locally improved breeding lines as potential donors for resistance breeding to C. lindemuthianum in Kenya.   Key words: Anthracnose, sequence characterized amplified region (SCAR), marker assisted selection (MAS).

Effectiveness of Anonidium mannii seed extracts against Colletotrichum lindemuthianum and Fusarium solani, agents responsible for anthracnose and fusariose of common beans (Phaseolus vulgaris L.) in the Centre region-Cameroon

Anthracnose and Fusariose of beans caused by Colletotrichum lindemuthianum and Fusarium solani respectively are two dreaded diseases that can lead to yield losses of 30 to 100% in the field. The present study was carried out to evaluate the antifungal activities of seed extracts of Anonidium mannii (Annonaceae) on the in vitro growth of C. lindemuthianum and F. solani. Extracts of A. mannii seeds obtained from acetone, water and methanol solvents, were used for phytochemical screening and for the preparation of solutions with concentrations of 12.5, 25 and 50 µl/ml. To evaluate radial growth, explants of 0.7 cm diameter each were obtained from two strains of C. lindemuthianum and two strains of F. solani. They were placed each at the centre of sterile Petri dishes containing the PDA medium supplemented with the different concentrations of extracts and incubated at 23°C for 6 days. The results of the phytochemical screening revealed the presence of alkaloids, phenols, saponins in the A. mannii seed extracts and this depended on the solvent used. The minimum inhibitory concentrations (MIC50 and MIC90) were also calculated. At a concentration of 50µl/ml each, acetone extract inhibited the growth of strain 2 of C. lindemuthianum (2.33 cm) more than the methanol extract (3.26 cm) in six days of incubation. Similarly, the growth of strain 2 of F. solani was strongly inhibited by methanol extract (1.98 cm). The MIC50 of the aqueous extract gave 27.38 µl/ml with F. solani and 32.24 µl/ml for the acetone extract with C. lindemuthianum. Due to their antifungal power, after purification with bioactive compounds, the aqueous, acetone and methanol extracts revealed by the phytochemical screening could be used as synthetic fungicides for the control of anthracnose and fusariose of common bean.

Genetic diversity of Colletotrichum lindemuthianum races based on ITS-rDNA regions

Colletotrichum lindemuthianum is the causal agent of anthracnose in common bean. Favorable conditions for this disease might result in up to 100% yield losses. One of the main challenges for common bean producers and breeders still remains the management disease, since this pathogen exhibits a wide genetic variability probably due to its recombination sexual reproduction. The 5·8S gene and the flanking internal transcribed spacer regions (ITS1 and ITS2) of 40 different isolates of C. lindemuthianum collected in Brazil were amplified by PCR, and sequenced in order to determine genetic variability. The results revealed that 46.88% of SNPs were detected in the ITS1 region, while 53.12% of them were located in the ITS2 region. The genetic distance ranged from 0.000 to 0.169 between races. The greatest distance was observed between the races 10 and 73 with a value of 0.169, indicating a wide genetic variability between them. The phylogenetic tree was composed of three groups. Group I had five subgroups. Similar results were also observed through population structure analysis, which revealed the presence of three clusters. These results suggest that sequence analysis of ITS rDNA regions of C. lindemuthianum may be a valuable tool to identify this pathogen through design of specific primers.

POTASSIUM FERTILIZATION MANAGEMENT IN COMMON BEAN PROTECTION AGAINST COLLETOTRICHUM LINDEMUTHIANUM

Anthracnose of common bean caused by the fungus Colletotrichum lindemuthianum is considered one of the most important fungal diseases that attacks the aerial part of the common bean for causing significant losses in final productivity. Potassium is one of the elements that is involved in the defense of the plant. Thus, the objective was to evaluate the effect of potassium doses in the control of anthracnose in three common bean cultivars. The design used was completely randomized with five treatments in three repetitions. The severity of the disease was obtained at 15 days after inoculation using a diagrammatic scale of notes and by counting the number of lesions in the central and lateral leaflets and the length of the lesions in the midrib of the central leaflet.

Histochemical changes induced by Trichoderma spp. and potassium phosphite in common bean (Phaseolus vulgaris) in response to the attack by Colletotrichum lindemuthianum

Induction of resistance in common bean (Phaseolus vulgaris) has been considered a promising alternative to control anthracnose. Among the changes generated in the induction of resistance, structural changes have been reported by several authors as an efficient form of resistance to the stress plants undergo. Histochemical analysis techniques have been used to investigate tissue changes triggered by induction of resistance. Thus, this study aims to investigate certain histochemical changes suffered by common bean plants induced with potassium phosphite and Trichoderma spp. in response to the attack by Colletotrichum lindemuthianum, aiming to determine the host response pattern in terms of structural changes, associating it to possible disease control. Treatments consisted of isolates T. harzianum (isolate TOD1) and T. virens (isolate TM4), leaf fertilizer potassium phosphite Fertilis®, and distilled water (control). Inducers were applied to common bean alone or associated, consisting of five treatments plus the control treatment. The six treatments were evaluated for the absence and presence of C. lindemuthianum in a factorial scheme (6×2). Treatments allowed evaluating the severity of anthracnose in common bean, location of H2O2, lignin deposition, and hypersensitivity response in common bean hypocotyl by histochemical staining. Potassium phosphite and combinations of T. virens and T. harzianum with potassium phosphite efficiently reduced disease severity under greenhouse conditions, reaching 68, 84, and 71%, respectively. Studies with hypocotyl showed that T. harzianum + potassium phosphite and T. virens + potassium phosphite accelerated the H2O2 accumulation process and lignin deposition at the pathogen penetration site, in addition to the hypersensitivity reaction through the resistance-inducing activity, contributing to the protection of common bean against anthracnose caused by C. lindemuthianum.

English

Common bean is among the most important legume crop for protein source in people’s diet globally and including Kenya. Anthracnose is a common disease of legumes that causes yield loss of up to 90-100%. The aim of the study is to investigate the morphological traits associated with anthracnose resistance in selected common bean genotypes in Kenya. The study was done in three varied agro-ecological zones; University of Eldoret, Bungoma and Busia. Fifteen genotypes were evaluated on field experiment to ascertain morphological traits associated with anthracnose resistance. Field experiment was done in a random complete block design. Data were collected on morphological traits and subjected to analysis of variance in SAS version 9.1. The genotypes, Ciankui, Tasha, KK15, KK8, Miezi mbili and Chelalang showed morphological traits that were significantly (P ≤ 0.05) associated with anthracnose resistance, and also with high grain yields of 1.5 to 2.0 t/ha.  Morphological traits associated with common bean anthracnose resistance included Leaf width, leaf length, length of fifth internode of the stems, bracteolate size classification and flower colour. It is recommended that management of anthracnose by use of resistant common bean genotype seeds is essential to provide increased bean yields globally and in Kenya.   Key words: Common bean, anthracnose, morphological traits, resistance.

Evaluation of Common Bean (Phaseolous vulgaris L.) Varieties for the Reaction of Common Bean Anthracnose (Colletotrichum lindemuthianum) at Sirinka, Eastern Amhara, Ethiopia

Common bean (Phaseolous vulgaris L.) is the most important food legume consumed as source of protein and cash crop in Ethiopia. The production of the crops is constrained by biotic and abiotic factors. Common bean anthracnose caused by the fungus Colletotrichum lindemuthianum is a major production constraint in common bean growing regions of Ethiopia. Field experiment was conducted at Sirinka Agricultural research center during 2017/18 main cropping season to evaluate reactions of common bean varieties to the disease. The experiment consisted of twenty two common bean varieties evaluated for the reaction to anthracnose under natural infestation conditions. The highest disease severity (58%) was recorded from Awash-1 variety while the lowest disease severity (45%), was recorded from Awash Melka variety at final assessment day. The highest (3.03 t ha-1) yield was recorded from Awash Melka variety while the lowest (0.97 t ha-1) yield was recorded from KAT-B1 variety. From the present study, it is possible to conclude that, the advantage of screening resistant verities increases the opportunity to select for a broad range of anthracnose resistance and help to know the variability of the common bean anthracnose disease.

Interaction between Bean and Colletotrichum gloeosporioides: Understanding Through a Biochemical Approach.

In addition to its role in animals, nowadays nitric oxide (NO) is considered as an emerging signaling molecule in plant systems. It is now believed that NO exerts its pivotal role in various plant physiological processes, such as in seed germination, plant developmental stages, and plant defense mechanisms. In this study, we have taken an initiative to show the biochemical basis of defense response activation in bean leaves during the progression of Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. in detached bean leaves. Stages of pathogen penetration and colonization were successfully established in the detached bean leaves. Results showed up-regulation of different defense-related enzymes and other defense molecules, such as phenols, flavonoids, callose, and lignin molecules, along with NO at early stages of pathogen invasion. Although in the later stages of the disease, development of NO and other defense components (excluding lignin) were down-regulated, the production of reactive oxygen species in the form of H2O2 became elevated. Consequently, other stress markers, such as lipid peroxidation, proline content, and chlorophyll content, were changed accordingly. Correlation between the disease index and other defense molecules, along with NO, indicate that production of NO and reactive oxygen species (ROS) might influence the development of anthracnose in common bean.

Effect of Intercropping and Compost Application for the Management of Common Bean Anthracnose ( Colletotrichum lindemuthianum ) in North Shewa, Central Ethiopia

Common bean is grown for its high nutritive, medicinal and market value in Ethiopia. Anthracnose is among the major production constraint within central common bean producing regions of Ethiopia. Field experiments were conducted on two common bean varieties Awash Melka and Mexican 142 at Shewarobit and Ataye in 2016 and 2017 main cropping seasons with the objective of evaluating the effects of row intercropping, compost plus their integration on disease severity of common bean anthracnose. Field experiments revealed maximum disease severity on highly susceptible variety Mexican 142 than Awash Melka at both locations and during both cropping seasons. Significantly, the lowest (26.9%) mean final anthracnose severity was obtained from the integration of intercropping with compost application at Ataye during 2017 and (562% day) mean area under disease progress curve was obtained from the integration of intercropping with compost application at Shewarobit during 2017. Whereas significantly the highest (39%) mean final disease, severity and (849% day) mean AUDPC were recorded from the sole planting control plots in 2016 at Shewarobit. Integration of intercropping with compost application as ecofriendly disease management option was the appropriate management option of common bean anthracnose in the study area. Further studies of integrating management options need to be conducted to reduce the residual effects of agrochemicals.