Test Cultivars Research Articles

Field evaluation of a modified augmented design for early stage selection involving a large number of test lines without replication

The modified augmented design, recently proposed as a method of adjusting for environmental heterogeneity where large numbers of cultivars are being tested in non-replicated plots, was used in a potato breeding programme at four locations in 1982. Of three methods of adjusting for soil variation, only the row-column and covariance adjustments worked efficiently. Decisions about which adjustment method to use could be based on easily computed mean squares. Changes in ranking due to adjustment of test cultivars were large in three of the seven trials, but application of inappropriate adjustment methods produced large and misleading ranking changes in some trials. Because of ease of use and ability to investigate environmental variation, the design can be recommended for use in early stages of potato breeding programmes.

Genetic Analysis of Resistance to Green Leafhopper in Rice

AbstractThe inheritance of resistance to green leafhopper, Nephotettix impicticeps Ichi, was studied in 11 cultivars of rice, Oryza saliva L. These resistant cultivars were crossed with the susceptible cultivar ‘TN1’. The materials consisted of F1, F2 and F3 populations including parents which were assessed by the bulk screening test. It was found that resistance in the cultivars TR36′, UPR254‐35‐3′‐2′, ‘Jhingasail’, ‘Govind’, ‘RP825‐45‐1‐3’, ‘MRC603‐303’, ‘RD4’, and ‘Irat104’ was conditioned by a single dominant gene, whereas resistance in ‘Ptb8’ IR9805‐97‐1′, and ‘BG367‐7’ was controlled by one recessive gene.The test on the allelic relationships of the resistance genes in the test cultivars with the known genes Glb1 and Glb2 revealed that the single dominant gene that conveyed the resistance in ‘UPR254‐35‐3‐2’ and ‘Jhingasail’ was allelic to Glh1 and segregated independently of Glh2. The resistance in ‘Govind’ and ‘RP82S‐45‐1‐3’ was governed by the Glh2 gene which was independent of Glh1. The test cultivars ‘IR36’;. ‘MRC603‐303’, ‘RD4’. and Irat104’ had a dominant gene for resistance which was nonallelic to Glb1 and Glb2. The recessive gene which conditioned the resistance in ‘Ptb8’, ‘IR9805‐97‐1’, and ‘BG367‐1’ segregated independently of Glh1 and Glh2.Eleven trisomics in an ‘TR36’ background were crossed with ‘Java’, a cultivar susceptible to green leafhopper. The segregation pattern of the F2 and backcross generations revealed that the Glb6 gene was located on chromosome 5.

Apple, Insect and Mite Control, 1986

Abstract Test materials were applied to 20- to 30-year-old apple trees at Monmouth, Maine, as dilute sprays using a hand gun and a hydraulic sprayer operating at 250 psi at 350 (Test 1) to 400 gal/acre. Trees were sprayed on 10 May (prepink, PP), 28 May (petal fall, PF), 12 Jun (first cover, IC), 24 Jun (second cover, 2C), 7-8 Jul (third cover, 3C), 22-24 Jul (fourth cover, 4C), 5 Aug (fifth cover, 5C), 20-21 Aug (sixth cover, 6C), as noted in the table. The fungicide program consisted of Difolatan 4F (5 qt/100) on 25 Apr (quarter-inch green), Captan 80W (1 lb) plus Benlate 50W (4 oz) on 21 May (bloom) and with Funginex 1.6EC (13 oz) on 26 May and Polyram 80W (2 lb) which was mixed with each insecticide treatment at each spray date. There were 4 single tree replicates for each treatment. A randomized complete block design was used with 2 ‘Mcintosh’ and 2 ‘Cortland’ cultivars in Test 1 and 4 ‘Mcintosh’ in Test 2. Except for test trees, the orchards were not sprayed with insecticides or acaricides. On 28 Aug, about 450 apples were picked from the 4 trees of each treatment and examined on 6 Sep for external egg punctures (AM), egg-laying scars (PC), and typical feeding injuries (CM, LAW, and TPB). ERM were counted on 25 leaves collected at chest-height around the periphery of each tree. Leaves were brought into the laboratory and brushed onto glass plates coated with a Tween 20 and alcohol mixture; mites were counted the same day. Aphid counts were based on 10 randomly selected vegetative terminals around each tree. Numbers of live aphids on the distal 4 unfurled and 1 furled leaves and on the stem included by these leaves were recorded on 23 Jul (Test 1). Although May was fairly warm and wet, the rest of the season was cool and wet, especially the first half of Aug (4.8 inches rain). At least a trace of rain was recorded for over half the days during the season.

Apple, Insect and Mite Control, 1985

Abstract Test materials were applied to 19- to 29-year-old apple trees at Monmouth, Maine, as dilute sprays using a hand gun and a hydraulic sprayer operating at 250 psi at 300 gal/acre. Trees were sprayed on 16 May (pink, P), 28-29 May (petal fall, PF), 14 Jun (first cover, 1C), 25-26 Jun (second cover, 2C), 9 Jul (third cover, 3C), 23-24 Jul (fourth cover, 4C), 6 Aug (fifth cover, 5C), 20 Aug (sixth cover, 6C), as noted in the table; the Rotacide treatment (3C-9C) was applied only on 9 Jul, 17 Jul, 25 Jul, 2 Aug, 8 Aug, 15 Aug, and 22 Aug. The fungicide program consisted of Difolatan 4F (5 qt/100) on 24-28 Apr and Polyram 80W (2 lb) which was mixed with each insecticide treatment at each spray date; no Polyram mixtures were made with the Rotacide treatment (3C-9C). There were 3-4 single tree applications for each treatment. A randomized complete block design was used with 2 ‘Mcintosh’ and 2 ‘Cortland’ cultivars in Test 1 and 4 ‘Mcintosh’ in Test 2. Except for test trees, the orchards were not sprayed with insecticides. On 28 Aug, 0.5 box of apples was picked from each tree (only 3 trees were sampled in Test 2), and about 520 (Test 1) or 180-370 (Test 2) apples were examinee1 per treatment on 7 to 14 Sep for external egg punctures (AM), egg-laying scars (PC), and typical feeding injuries (CM, LAW, and TPB). ERM were counted on 31 Jul and 15-16 Aug on 25 leaves collected at chest-height around the periphery of each tree. Leaves were brought into the laboratory and brushec onto glass plates coated with a Tween 20 and alcohol mixture; mites were counted the same day. Aphid counts are based on 10 randomly selected vegetative terminals around each tree. Numbers of live aphids on the distal 4 unfurled and 1 furled leaves and on the stem included by these leaves were recorded or 18 Jul and 1 Aug (Test 2). May and Jun were cool, the first half of Jul was wet (3.9 inches rain), and Aug was wetter (3.4 inches rain) and cooler than normal.

Pest control in maize: Search for source of resistance to stem borers

The relative response of 48 maize cultivars to infestation by stem borers, predominantly Sesamia calamistis Hmps., was determined in replicated small plot tests spanning 3 years (1975 to 1977) at Amakama. Cultivars showed ·no significant differences (P = 0.05) for average number of eggs/plant and mean % stand loss. The year effect was highly significant (P <0.01) for average number of eggs/plant and mean % stand loss. Cultivar x year interaction was not significant for both characters. Gravid moths deposited from 0.3 to 5.1 eggs/plant, apparently preferring Poey B 15, Poey T 84, Bulk-3, Inia VS 450, FARZ 23, and Onitsha to Ikom, UCA, Okoma, ICA H302, and H-101. Larval feeding injury caused the loss of 38.1 to 87.7% of the population of maize stands established, showing that none of the test cultivars has the potential to serve as a source of genes conferring resistance against borers. Ikom and Inia VS 450 were the least susceptible to borer feeding injury.

Prevention of rice tungro virus disease and control of the vector with granular insecticides

SUMMARYThirteen granular insecticides were screened under glasshouse conditions for their ability to kill the vector, Nephotettix virescens, and to prevent tungro virus infection. Carbofuran, bendiocarb, isoprocarb, BPMC, disulfoton, mephosfolan and phorate caused 100% vector mortality, but only the first four reduced virus infection to an acceptable level; the remainder killing the vector too slowly to prevent virus transmission. Seven of these compounds were evaluated in the field on two test cultivars, Traichung Native 1 and Pankaj. Carbofuran, isoprocarb and BPMC gave acceptable control of the disease on both cultivars and diazinon on cv. Pankaj only.

Technique for Locating Planthopper (Homoptera: Delphacidae) and Leafhopper (Homoptera: Cicadellidae) Eggs in Rice Plants

Eggs of two species of planthoppers, Nilaparvata lugens (Stål) and Sogatella furcifera (Horváth), and a leafhopper, Nephotettix virescens (Distant), were revealed in situ in susceptible and resistant rice plants using a simple staining technique. Rice plants containing insect eggs were bleached in boiling water for 5–7 min, kept in 95% ethyl alcohol for 3 days, rinsed in water, and then immersed in 1% aqueous acid fuchsin solution for 2 days. Plants were then washed under running water until stained eggs were differentiated from destained plant tissue. Eggs were counted using a 20 × binocular microscope. Results indicated that indiscriminate egg laying by N. lugens, S. furcifera, and N. virescens females rendered all test cultivars equally suitable for oviposition; however, significantly fewer eggs hatched on resistant rice cultivars than on susceptible ones.

Factors affecting the development of cane blight (Leptosphaeria coniothyrium) on red raspberries in Washington, Scotland and Germany

SUMMARYThe effects of cultivar, virulence of isolates of Leptosphaeria coniothyrium, cane maturation and wound healing were examined in a series of inoculation experiments carried out over a 3–yr period in three countries in an attempt to explain why cane blight has caused serious yield losses in machine‐harvested red raspberries in Europe, but not in the Pacific Northwest of America. Three isolates of L. coniothyrium from Puyallup (USA), Dundee (UK) and Dossenheim (FRG) were pathogenic on the three test cultivars Willamette, Malling Jewel and Glen Isla in all the experiments. Isolates and cultivars differed for aggressiveness and susceptibility respectively but their ranking was dependent on the test conditions and the differences were small and unlikely to explain the differences in incidence and severity of cane blight in raspberry fields in Scotland and the Pacific Northwest. Conditions at Dossenheim were most favorable for lesion development. At all sites, canes inoculated in late summer produced shorter lesions than those inoculated earlier. A delay between wounding and inoculation produced shorter lesions than simultaneous wounding and inoculation.

Allelopathic suppression of weed and nitrification by selected cultivars ofSorghum bicolor (L.) moench

Root exudates of 100 cultivars ofSorghum bicolor L. (Moench) were screened for their ability to inhibit seed germination and seedling growth ofAmaranthus retroflexus L. Exudates of some of the test cultivars were found to inhibit significantly seed germination and/or seedling growth ofA. retroflexus, and most of the inhibitory activity was found in neutral and acetone fractions of root exudates. Testing of aqueous extracts and decaying residues of four selectedSorghum cultivars (two toxic and two nontoxic through root exudation) revealed that all four cultivars significantly reducedA. retroflexus growth and nitrification processes with greater inhibition achieved by the toxic cultivars. This study suggests a potential biological control ofAmaranthus and nitrification by someS. bicolor cultivars.

Behavioral and Physiological Responses of Sogatella furcifera (Homoptera: Delphacidae) to Selected Resistant and Susceptible Rice Cultivars

Various behavioral and physiological responses involved in establishment of a planthopper, Sogatella furcifera (Horvath), on rice cultivars with diverse resistance genes were investigated. The cultivars tested were resistant ‘Muskhan 41’ ( Wbph 1), ‘N22’ ( Wbph 1), ‘N32’ ( Wbph 1), ‘ARC 10239’ ( Wbph 2), ‘ADR 52’ ( Wbph 3), ‘Podiwi A8’ ( Wbph 4), ‘wc 1240’ ( Wbph 1 + 1 recessive ?), ‘Colombo’ ( Wbph 2 + 1 recessive ?), ‘IR2035-117-3’ ( Wbph 1 + Wbph 2), and the susceptible ‘Taichung Native l’ (TN1) (no resistance gene). In a free-choice test, the orientational response of S. furcifera females due to visual attraction was identical on resistant and susceptible cultivars, but after 8 h, significantly more individuals settled on susceptible TNI plants than on resistant ones. The quantity of food ingested and assimilated by S. furcifera on resistant cultivars was significantly less than on susceptible TN1;. The suitability of TN1 plants for S. furcifera growth was highest among all test cultivars. A significant reduction in adult survival and fecundity, egg hatchability, and population increase was observed on resistant plants compared with susceptible TN1; however, oviposition was not affected. A comparison of the relative intensity of S. furcifera responses toward different resistant cultivars revealed that ‘IR2035-117-3’ was least suitable for the insect’s establishment, whereas ‘Podiwi A8’ had the lowest level of resistance.

PROCEDURAL APPROACH FOR ASSESSING CULTIVAR-LOCATION DATA: PAIRWISE GENOTYPE-ENVIRONMENT INTERACTIONS OF TEST CULTIVARS WITH CHECKS

A simple procedure for assessing cultivar-location data is proposed. The procedure consists of comparisons between checks and each of the test cultivars to find those test cultivars for which comparison with the checks can be done ignoring variability among locations, and to isolate those for which a location-by-location comparison is advisable. Since the level at which a comparison-wise genotype-environment interaction is deemed to be important can be set by the user, this represents a great simplification of the assessment process. A set of regional trial data was used as an example to demonstrate the approach. The complementary nature of this method with cluster analyses which group cultivars or locations is discussed.Key words: Genotype-environment interaction, cultivar assessment, barley yield

DESIGN AND MODEL FOR INVESTIGATING COMPETITION EFFECTS FROM NEIGHBOURING TEST PLOTS

A non-random design was proposed for studying competition effects from neighboring plots. In order to minimize the number of plots, the design utilizes every plot as a test plot as well as a border plot. When the number of cultivars is odd, the number of plots required for one replication equals the number of competition treatments (i.e. the number of distinct triplets of cultivars) plus two. The proposed competition model enables the scientist to investigate the additive and non-additive competition effects. The former can be further investigated for complementarity of the effect between test and competitor cultivars. For the latter, qualitative (different cultivars on both sides) and quantitative (the same cultivar on both sides) aspects of competition can be investigated. An experiment employing the proposed design with soybean cultivars was analyzed.Key words: Non-random design, border effect, competition effect

Oviposition and infestation of the sorghum shootfly, Atherigona soccata Rondani, on certain sorghum cultivars in relation to their relative resistance and susceptibility

Sorghum shootfly, Atherigona soccata, oviposition and infestation on eight resistant sorghum cultivars (IS nos: 2122, 2123, 2205, 2291, 4660, 5092, 5480 and 18551) and two susceptible cultivars (Serena and CSH-1), were studied under field conditions (natural infestation). The eight resistant cultivars and CSH-1 were also tested for preference for oviposition in a two-choice situation in the screenhouse. The eight resistant cultivars received considerably less shootfly eggs and showed fewer “dead hearts” than the susceptible cultivars. The results indicate that non-preference for oviposition is an important mechanism for resistance to shootfly in eight test cultivars. There was also evidence for a certain degree of antibiosis in IS 2291.

A New Dominant Gene for Resistance to Whitebacked Planthopper in Rice1

The mode of inheritance and allelic relationships of genes for resistance to whitebacked planthopper, Sogatella furcifera (Hbrvath), in 15 resistant cultivars of rice, Oryza sativa L., were studied. One‐leaf stage seedlings were artificially infested with second‐ and third‐instar whitebacked planthopper nymphs. Reactions of the seedlings were recorded when the susceptible check, ‘Taichung Native 1’, (TN1) was completely killed. The reactions of F1, F2, and F3 progenies from the crosses of test cultivars with TN1 revealed that single dominant genes confer resistance in ‘Boegi Boera’, ‘DD4’, PI 184675‐6, ‘Siam Garden’, ‘Rening’, ‘N'Diang Marie’, ‘Manggar’, ‘Oha’, ‘Gokhue Saier’, ‘Tjempo Tolo’, and ‘Nemai‘. Two independent dominant genes govern resistance in ‘ARC5752’, ‘Chaia Anaser’, ‘Katuyhar Dhan’, and ‘Dhera Dun Basmati’. Tests for allelism revealed that the single dominant genes in Boegi Boera, DD4, PI 184675‐6, Siam Garden, Rening, Oha, Gokhue Saier, Tjempo Tolo, and Nemai, and one of the two independent dominant genes in ARC5752, Chaia Anaser, Katuyhar Dhan, and Dhera Dun Basmati are allelic to Wbph 1, and that the second gene in ARC5752 is allelic to Wbph 2. The second gene in Chaia Anaser, Katuyhar Dhan, and Dhera Dun Basmati was allelic to Wbph 3. The single dominant genes of N'Diang Marie and Manggar segregated independently of Wbph 1, Wbph 2, and Wbph 3. The dominant gene of N'Diang Marie was designated an Wbph 5. The allelic relationships of the dominant gene from Manggar to Wbph 5 are not known.

Apple, Mite Control, 1984

Abstract Test chemicals were applied to 7- to 23-year-old apple trees at Monmouth, Maine, as dilute sprays using a hand gun and a hydraulic sprayer operating at 250 psi and at 300 to 400 (Test 2) gal/acre. Spray dates were 15 May (tight cluster), 3 Jun (petal fall), 13 Jun (first cover), and 6, 13, and 18 Jul. The standard pesticide program consisted of Difolatan 4F (5 qt/100 gal) on 29 Apr, Polyram SOW (1.8 lb) on 3 dates, Captan 80W (0.9 lb) plus Benlate 50W (2.9 oz) on 2 dates, Imidan 50W (1 lb) on 2 dates, and Sevin 80W (1 lb) on 3 dates. These were no mixtures of acaricides with other pesticides. There were 4 single-tree replications for each treatment. A randomized complete block design was used, with 3 ‘Red Delicious’; and 1 ‘Cortland’ cultivars in Test 1, 2 ‘Red Delicious’ and 2 ‘Cortland’ cultivars in Test 2, 4 ‘Cortland’ cultivars in Test 3, and 3 ‘McIntosh’ and 1 ‘Golden Delicious’ cultivars in Test 4. From each tree 25 leaves were collected at chest-height around the periphery of the tree, brought into the laboratory, and brushed onto glass plates coated with a Tween 20 and alcohol mixture; mites were counted the same day. Minimum temperatures of 36°-37°F were recorded on the 4 days following the tight cluster treatments, and maximum temperatures of89°-90°F occurred on the 2 days after the treatments on 13 Jul. Although the last half of Jun was wet (3.0 inches rain), Jul and Aug were dry (1.8 and 1.5 inches, respectively).

Apple, Kelthane Applications, 1984

Abstract Test chemicals were applied to 28-year-old apple trees at Monmouth, Maine, as dilute sprays using an airblast sprayer operating at 200 psi and at 300 gal/acre. Spray dates were 22 May (pink), 4 Jun (petal fall), 13 Jun (first cover), and 6 and 13 Jul. The standard pesticide program consisted of Difolatan 4F (5 qt/100 gal) on 29 Apr, Phygon 50W (0.5 lb) on 1 Jun, Polyram 80W (2 lb) and Amid-Thin W (12 ppm) on 13 Jun, and Cyprex 65W (0.75 lb) on 29 Jun and 3 Jul. There were no mixtures of acaricides with other pesticides. Each treatment was applied to a block of 5 to 6 trees in which mite counts were made on 2 ‘McIntosh’ and 2 ‘Red Delicious’ cultivars in Test 1, and 2 ‘Cortland’ and 2 ‘Red Delicious’ cultivars in Test 2. From each tree 25 leaves were collected at chest-height around the periphery of the tree, brought into the laboratory, and brushed onto glass plates coated with a Tween 20 and alcohol mixture; mites were counted the same day. On days 3 to 5 following petal fall treatments, maximum daily temperatures ranged from 86°-95°F, and on day 3 following first cover treatments, minimum was 41°F. Maximum temperatures of 89°-90°F occurred on the 2 days after treatments on 13 Jul. The first half of Jun was warm and the last half was wetter than normal (3.0 inches rain); Jul and Aug were dry (1.8 and 1.5 inches rain, respectively).

Comparison between Free‐Choice and No‐Choice Seedling Bulk Tests for Evaluating Resistance of Rice Cultivars to the Whitebacked Planthopper1

During a screening of rice, Oryza sativa L., cultivars for resistance to the whitebacked planthopper Sogatella furcifera (Horváth) by the routinely used free‐choice seedling bulk test, a significantly higher insect population was observed to move over to the susceptible check cultivar soon after infestation. This uneven distribution of insects caused unbalanced infestation among the test cultivars. To avoid this shortcoming, a no‐choice seedling bulk test was conducted in which each row of test cultivar seedlings was excluded from the other by an intervening, vertical, mylar plastic partition, and was exposed to equal insect infestation. The resistance scores of 10 genetically diverse cultivars—‘Muskhan 41’ (Wbph 1), ‘N22’ (Wbph 1), ‘N32’ (Wbph 1), ‘ARC 10239’ (Wbph 2), ‘ADR 52’ (Wbph 3), ‘Podiwi A8’ (wbph 4), ‘Colombo’ (Wbph 2 + 1 recessive ?), ‘WC 1240’ (Wbph I + 1 recessive ?), ‘1R 2035‐117‐3’ (Wbph 1 + Wbph 2), and ‘Taichung Native 1’ (no resistance gene)—from free‐choice and no‐choice seedling bulk tests were compared. Podiwi A8 and N22, rated as moderately resistant and resistant in the free‐choice test, proved to be susceptible and moderately resistant, respectively, in the no‐choice test.The no‐choice test ensures an even distribution of test insects on cultivars and excludes any possibility of their escape from infestation. The technique has important implications in screening for resistance against a number of mobile insect pest species on a wide variety of plants.

Activity of Adult Whiteflies (Homoptera: Aleyrodidae) Within Plantings of Different Cotton Strains and Cultivars as Determined by Sticky-Trap Catches

Adults of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the bandedwinged whitefly, Trialeurodes abutilonea (Haldeman), were collected with sticky traps from replicated field plots of a number of different breeding stocks and cultivars of cotton, Gossypium hirsutum L., grown in three tests in Arizona and California. These cottons carried different combinations of the mutant characters nectariless, okra leaf, smoothleaf, and semismoothleaf. Many more B. tabaci than T. abutilonea were caught. None of the breeding stocks or test cultivars had fewer whiteflies than the cultivar ‘Deltapine 61;’ ‘Deltapine 62,’ however, attracted fewer B. tabaci. Smoothleaf in ‘AET-5’ background (‘AET-5’ is a breeding stock having resistance to the pink bollworm, Pectinophora gossypiella [Saunders]) had significantly fewer adults of both whitefly species than did pubescent-leaf plants. The nectariless and okra-leaf characters showed no significant differences, except that more bandedwinged whiteflies used okra leaf than its normal-leaf counterpart. Semismoothleaf yielded mixed results, suggesting that this character might be of some value for reducing whitefly populations if incorporated into an appropriate genetic background. Both okra leaf and nectariless okra leaf conferred some susceptibility to whiteflies in certain genetic backgrounds. This is a cause for concern because these two mutant characters impart resistance to pink bollworms.

THE PRECISION OF CULTIVAR TRIALS WITHIN EASTERN COOPERATIVE TESTS

Historical data from Eastern Cooperative tests (1977–1982) were used to find the distributional pattern of participating stations (locations) with respect to the coefficient of variation (CV) and D, the difference between the best check cultivar and the best test cultivar expressed as percentage of the mean at each location. The average CV in these cooperative tests is about 12%, which is adequate for detecting D values greater than 15% only. However, differences of this magnitude occur in no more than about 19% of the trials. To be able to have a good chance of detecting a difference of 5% within locations, (68% and 56% of recent trials for barley and oats respectively had D values greater than 5%), the present level of CV should be cut by up to half.Key words: Precision, cooperative tests, coefficient of variation

Use of cypermethrin, a synthetic pyrethroid, in the control of rice tungro virus disease and its vector

Abstract Out of 27 emulsifiable concentrate insecticides tested in the glasshouse, cypermethrin, vamidothion, FMC 35001, phosphamidon and demeton‐S‐methyl not only effectively prevented tungro virus infection but also killed the vector Nephotettix virescens (Dist.). Although dichlorvos, phosalone and phenthoate killed the vector efficiently they failed to prevent virus infection. Of the seven selected insecticides tested under field conditions, using Taichung (Native) 1 and Ratna as test cultivars, cypermethrin controlled tungro disease very efficiently and reduced the rate of tungro infection in the susceptible cultivar Taichung (Native) 1. Plant height, panicle number, grain yield and dry straw weight increased several fold in the cypermethrin‐treated plots in comparison to the control and other insecticides. Cypermethrin, acephate, FMC 35001, phosphamidon and demeton‐S‐methyl were very effective in controlling tungro disease and increased grain yield in Ratna, the tolerant cultivar. The vector populati...