Assessment of the losses caused to potatoes by the potato cyst nematodes, Globodera rostochiensis and G. pallida

Nine field trials were carried out from 1967 to 1973 on sandy loam soils in Staffordshire and Worcestershire to study the relationship between potato yield and numbers of potato cyst nematodes (Globodera spp.). Three (probably five) of these trial sites appeared to be infested with G. rostochiensis only, whereas both species occurred on the remaining four sites which grew the resistant variety, Maris Piper. Although mixtures of the two species occurred on some plots they tended to have different distributions within each trial site. The results from this work have been analysed, together with those from earlier work in the Eastern Counties on peat and silt soils, over two population density ranges, 0–40 eggs/g (5 sites) and 0–160 eggs/g (16 sites). There is no evidence of any difference in the regression of yield on eggs/g amongst the five sites in the lower range (b =–0.90 + 0.11) nor amongst 15 of the 16 sites in the higher range (b = -0–40 ± 0–02). Analysis of 10 sites with sufficient data in the 40–160 eggs/g range gave b = -0.24 ± 0.06. Thus the regression lines are essentially parallel for each of the two ranges, covering several potato varieties, soil textures and different potential yields and suggest that the varieties used are equally tolerant. The losses are 6.25 t/ha/20 eggs/g for the 0.40 eggs/g range, 1.67 t/ha/20 eggs/g for the 40–160 eggs/g range, and 2.75 t/ha/20 eggs/g as a mean for the whole range. A maximum loss of 22 t/ha is indicated. Peat soils are less dense than mineral soils but there was no need for adjustment in nematode counts. Losses caused by potato cyst nematodes are better expressed as actual yield losses rather than as percentage decreases.     

The effect of small doses of nematicides on migratory root-parasitic nematodes and on the growth of sugar beet and barley in sandy soils

Smaller amounts of D–D (6–12 gal/acre) (68–135 1/ha) or ethylene dibromide (9 gal/acre) (100 1/ha) than are customarily used to disinfest field soils killed many root-parasitic nematodes (Trichodorus, Pratylenchus, Tylenchorhynchus and Longidorus attenuatus) when injected 6–8 in (15–20 cm) deep during early autumn in rows 10 in (25 cm) apart in well-drained sandy soils. They also increased the yield of sugar beet grown in fields infested with Trichodorus or Longidorus attenuatus, without affecting sugar percentage or juice purity of the roots, and in some places increased the yield of barley grown after the beet. D–D was much less effective when injected 8–12 in deep during late autumn or winter. Increasing nitrogen dressings to the seedbed from 1·5 to 3 cwt/acre (188 to 376 kg/ha) increased sugar beet yield in one field, decreased it in another and decreased juice purity in both. In two other experiments extra nitrogen did not affect sugar beet yield. Even smaller amounts of the nematicides ‘placed’ in the rows, before or after sowing sugar beet in them, killed many of the nematodes and also increased sugar yield. Phytotoxic nematicides can be placed in the rows during autumn, winter or spring but placement is simpler during spring, when the treated rows are indicated by the position of the marks of the tractor wheels left when the nematicide was applied. When applied during autumn or winter, the rows need to be indicated by drilling wheat or grass.     

Suppression of Heterodera schachtii Populations by Dactylella oviparasitica in Four Soils

The effects of Dactylella oviparasitica strain 50 applications on sugarbeet cyst nematode (Heterodera schachtii) population densities and plant weights were assessed in four agricultural soils. The fungus was added to methyl iodide-fumigated and nonfumigated portions of each soil. The soils were seeded with Swiss chard. Four weeks later, soils were infested with H. schachtii second-stage juveniles (J2). Approximately 1,487 degree-days after infestation, H. schachtii cyst, egg and J2 numbers and plant weights were assessed. In all four fumigated soils, D. oviparasitica reduced all H. schachtii population densities and increased most of the plant weights compared to the nonamended control soils. In two of the nonfumigated soils (10 and SC), D. oviparasitica reduced H. schachtii population densities and increased most plant weight values compared to the nonamended control soils. For the other two nonfumigated soils (44 and 48), which exhibited pre-existing levels of H. schachtii suppressiveness, fungal applications had relatively little impact on H. schachtii population densities and plant weights. The results from this study combined with those from previous investigations suggest that D. oviparasitica strain 50 could be an effective biological control agent.     

Chemical control of beet cyst-nematode, Heterodera schachtii, in some peaty loam soils

In peaty loam soils, aldicarb or oxamyl mixed with the top 15 cm of the soil in spring before sugar beet seeds were sown, minimised invasion of the roots by larvae of the beet cyst-nematode, Heterodera schachtii, so preventing injury to the seedlings, and greatly increased sugar yields in heavily infested soil. Small amounts of both compounds were often as effective as larger amounts. Nematode increase on sugar beet roots was slow. Aldicarb or oxamyl lessened nematode increase in four years out of five. Fumigating predetermined row positions with dichloropropene mixtures (D-D, Telone) or incorporating aldicarb or methomyl shallowly in soil, later occupied by the roots of sugar beet seedlings, did not control the nematode, although sugar yields were sometimes increased.     

Genetic approaches to sustainable pest management in sugar beet (Beta vulgaris)

Sugar beet (Beta vulgaris) is an important arable crop, traditionally used for sugar extraction, but more recently, for biofuel production. A wide range of pests, including beet cyst nematode (Heterodera schachtii), root‐knot nematodes (Meloidogyne spp.), green peach aphids (Myzus persicae) and beet root maggot (Tetanops myopaeformis), infest the roots or leaves of sugar beet, which leads to yield loss directly or through transmission of beet pathogens such as viruses. Conventional pest control approaches based on chemical application have led to high economic costs. Development of pest‐resistant sugar beet varieties could play an important role towards sustainable crop production while minimising environmental impact. Intensive Beta germplasm screening has been fruitful, and genetic lines resistant to nematodes, aphids and root maggot have been identified and integrated into sugar beet breeding programmes. A small number of genes responding to pest attack have been cloned from sugar beet and wild Beta species. This trend will continue towards a detailed understanding of the molecular mechanism of insect–host plant interactions and host resistance. Molecular biotechnological techniques have shown promise in developing transgenic pest resistance varieties at an accelerated speed with high accuracy. The use of transgenic technology is discussed with regard to biodiversity and food safety.     

Reproduction of Heterodera schachtii Schmidt on Resistant Mustard,Radish, and Sugar Beet Cultivars

The reproduction of a Wyoming population of Heterodera schachtii was determined for resistant trap crop radish (Raphanus sativus) and mustard (Sinapis alba) cultivars, and resistant and susceptible sugar beet (Beta vulgaris) cultivars in a greenhouse (21 °C/16 °C) and a growth chamber study (25 °C). Oil radish cultivars also were field tested in 2000 and 2001. In the greenhouse study, reproduction was suppressed similarly by the resistant sugar beet cultivar Nematop and all trap crop cultivars (P ≤ 0.05). In the growth chamber study, the radish cultivars were superior to most of the mustard cultivars in reducing nematode populations. All trap crops showed less reproduction than Nematop (P ≤ 0.05). In both studies, Nematop and all trap crops had lower Pf than susceptible sugar beet cultivars HH50 and HM9155 (P ≤ 0.05). In field studies, Rf values of radish cultivars decreased with increasing Pi of H. schachtii (r² = 0.59 in 2000 and r² = 0.26 in 2001). In 2000, trap crop radish cv. Colonel (Rf = 0.89) reduced nematode populations more than cv. Adagio (Rf = 4.67) and cv. Rimbo (Rf = 13.23) (P ≤ 0.05) when Pi was lower than 2.5 H. schachtii eggs and J2/cm³ soil. There were no differences in reproductive factors for radish cultivars in 2001 (P ≤ 0.05); Rf ranged from 0.23 for Adagio to 1.31 for Commodore for all Pi.     

Effect of Plant Age and Transplanting Damage on Sugar Beets infected by Heterodera schachtii

Sugar beet (Beta vulgaris L. cv. Monogerm C.S.F. 1971) seeds sown into Vineland fine sandy loam, infested with 15,500 H. schachtii juveniles/pot, showed little growth during an 11-week test in the greenhouse. Seedlings transplanted at 2, 4, and 6 weeks of age had 32, 30, and 31% less top weight and 71, 68, and 59% less root weight, respectively, compared to controls grown in nematode-free soil. Nematode reproduction in both direct-seeded and transplanted sugar beets was limited and related to root weight. Shoot/root ratios were increased by the nematodes in all nematode-infected beets compared to those grown in soil without nematodes. In contrast to seeding or transplanting sugar beets into nematode-infested Vineland fine sandy loam, an inoculation of Beverly fine sandy loam supporting 0 (seeds), 2-, 4-, and 6-week-old sugar beet seedlings with 7,400 juveniles/pot, followed by 11 weeks of growth in the growth-room, resulted in top weight losses of only 13, 3, 18, and 15% and losses in root weight of 44, 38, 36, and 38%, respectively. Nematode reproduction was high and all shoot/root ratios were increased by the nematode compared to the noninoculated controls. These experiments have shown that sugar beets sown into nematode-infested soil are damaged much more heavily by H. schachtii juveniles than seeds inoculated with the nematode immediately following sowing. Results indicate that an increase in tolerance of sugar beets to attack by H. schachtii does not occur beyond the first 2 weeks of growth and that transplanting damage lowers the tolerance of seedlings to nematode attack.     

Helicotylenchus vulgaris and its association with damage to sugar beet

Severe and irregular stunting of sugar beet has been associated with Helicotylenchus vulgaris but little is known of the pathogenicity of this nematode. A survey was made at 10 sites in East Anglia on calcareous soils (Wantage series) on which the original damage was reported. Numbers were usually maintained under a variety of crops, despite fluctuations during the period. In field trials, aldicarb treatment did not improve the yield of either sugar beet or winter wheat on land infested with H. vulgaris. In pot tests growth of sugar beet was stimulated by low nematode inocula; this effect diminished as numbers inoculated increased. Sugar beet grown at 10 °C and 15 °C with H. vulgaris grew markedly better in sterilised soil than in untreated field soil, especially at the higher temperature early in the experiment. It is concluded that though H. vulgaris may damage sugar beet it requires an atypical combination of external conditions to cause significant yield loss.     

The effect of resistant cultivars of catch crops on the hatching of Heterodera schachtii

In laboratory tests with Heterodera schachtii, root leachates of nematode-resistant and susceptible cruciferous crops stimulated egg hatches of up to 77% and 95% respectively. In these tests very little hatch occurred at 5°C or 10°C, more at 15°C and most at 20°C. In field experiments in which these crops were sown in September 1982 and August 1983 into soil infested with H. schachtii, numbers of viable eggs had decreased only slightly under resistant crops 4–5 months later. This was possibly because the soil was too cold and dry to permit a large proportion to hatch.     

Impact of soil suppressiveness on various population densities of Heterodera schachtii

Infectivity of second‐stage juvenile (J2) populations of Heterodera schachtii was assayed with radish.The numbers of J2 in three‐day‐old seedlings were proportional to the numbers of J2 in two differently textured soils.In a microplot trial with a known H.schachtii‐supprcssivc soil, half of the plots contained untreated suppressive soil, the other half contained the same soil, but methyl iodide‐fumigated and therefore conducive.Both soils were infested with cysts introducing the equivalents of 0, 30, 60 or 120 H.schachtii eggs g‐¹ soil, kept moist for 2 months, and then planted to Swiss chard.The numbers of J2 in radish roots were proportional to the numbers of H.schachtii eggs introduced into the microplots, at a low level of detection in suppressive soil and at a high level in conducive soil.Growth of Swiss chard was not different at increasing infestation levels in suppressive soil, but growth was reduced in conducive soil proportionally to increasing nematode infestation level.     

Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii

Sedentary plant‐parasitic cyst nematodes are obligate biotrophs that infect the roots of their host plant. Their parasitism is based on the modification of root cells to form a hypermetabolic syncytium from which the nematodes draw their nutrients. The aim of this study was to identify nematode susceptibility genes in Arabidopsis thaliana and to characterize their roles in supporting the parasitism of Heterodera schachtii. By selecting genes that were most strongly upregulated in response to cyst nematode infection, we identified HIPP27 (HEAVY METAL‐ASSOCIATED ISOPRENYLATED PLANT PROTEIN 27) as a host susceptibility factor required for beet cyst nematode infection and development. Detailed expression analysis revealed that HIPP27 is a cytoplasmic protein and that HIPP27 is strongly expressed in leaves, young roots and nematode‐induced syncytia. Loss‐of‐function Arabidopsis hipp27 mutants exhibited severely reduced susceptibility to H. schachtii and abnormal starch accumulation in syncytial and peridermal plastids. Our results suggest that HIPP27 is a susceptibility gene in Arabidopsis whose loss of function reduces plant susceptibility to cyst nematode infection without increasing the susceptibility to other pathogens or negatively affecting the plant phenotype.     

Failure of a Mycelial Formulation of the Nematophagous FungusHirsutella rhossiliensisto Suppress the NematodeHeterodera schachtii

Research was conducted to determine whether pelletized hyphae ofHirsutella rhossiliensissuppressed invasion of roots by the sugarbeet cyst nematodeHeterodera schachtiiin field microplots. The loamy sand in the microplots was infested withH. schachtiibut not withH. rhossiliensis.Alginate pellets, with or without hyphae ofH. rhossiliensis,were mixed into soil removed from the microplots (1 pellet/cm³of soil). The soil was placed in cylinders positioned vertically in microplots; cylinders (6/microplot) were 10.1 cm wide and 15.3 cm deep and contained 1200 cm³of soil. Pellets and soil also were placed in soil observation chambers, which were buried in the cylinders or kept at 20°C in moisture chambers in the laboratory. After 12 days, cabbage seeds were planted in each cylinder, and after 10 days of growth, the seedlings were removed from the soil andH. schachtiiin the roots were counted. The number ofH. schachtiiin roots was large and was unaffected by addition ofH. rhossiliensis.In soil observation chambers,H. rhossiliensisgrew vigorously from the pellets in heat-treated soil but not in nonheated soil, and enchytraeids and collembolans were observed near damaged pellets. We suspect that organisms, possibly including enchytraeids and collembolans, fed upon or otherwise inhibitedH. rhossil- iensis.     

Sporamin-mediated resistance to beet cyst nematodes (Heterodera schachtii Schm.) is dependent on trypsin inhibitory activity in sugar beet (Beta vulgaris L.) hairy roots

Sporamin, a sweet potato tuberous storage protein, is a Kunitz-type trypsin inhibitor. Its capability of conferring insect-resistance on transgenic tobacco and cauliflower has been confirmed. To test its potential as an anti-feedant for the beet cyst nematode (Heterodera schachtii Schm.), the sporamin gene SpTI-1 was introduced into sugar beet (Beta vulgaris L.) by Agrobacterium rhizogenes-mediated transformation. Twelve different hairy root clones expressing sporamin were selected for studying nematode development. Of these, 8 hairy root clones were found to show significant efficiency in inhibiting the growth and development of the female nematodes whereas 4 root clones did not show any inhibitory effects even though the SpTI-1 gene was regularly expressed in all of the tested hairy roots as revealed by northern and western analyses. Inhibition of nematode development correlated with trypsin inhibitor activity but not with the amount of sporamin expressed in hairy roots. These data demonstrate that the trypsin inhibitor activity is the critical factor for inhibiting growth and development of cyst nematodes in sugar beet hairy roots expressing the sporamin gene. Hence, the sweet potato sporamin can be used as a new and effective anti-feedant for controlling cyst nematodes offering an alternative strategy for establishing nematode resistance in crops.     

Effect of Criconemella onoensis on Potato

Criconemella onoensis (Luc) Luc and Raski increased to high (458-1,290/100 cm³) soil population densities in four fields planted to cover crops of sorghum-sudangrass (Sorghum bicolor (L.) Moench × S. arundinaceum (Desv.) Stapf var. sudanense (Stapf) Hitchc. ''Funk FP-4'') during the summer of 1984 in southeastern Florida. Three pathogenicity tests conducted in the greenhouse with C. onoensis on potato (Solanum tuberosum L. ''La Rouge'') using three different methods (inoculation, chemical treatment of infested soil, or pasteurization of infested soil) revealed no significant (P = 0.10) differences in plant growth, despite significant (P = 0.05) differences in population densities of C. onoensis between treated and control pots in each test. In these three tests, the maximum initial density of C. onoensis used was 720/100 cm³ soil and the maximum final density was 686/100 cm³ soil. Application of 933 liters/ha of Vapam to a field site with a pretreatment density of 1,120 C. onoensis/100 cm³ soil significantly (P = 0.05) reduced populations compared with untreated control plots, but yields remained higher in control plots. Apparently C. onoensis has no significant effect on potato growth at the population densities tested.     

Effects of Cycloate on Development of Heterodera schachtii and Growth of Three Beta Species

Greenhouse tests were set up to evaluate the effects of the herbicide, cycloate (S-ethyl cydohexylethylthiocarbamate), oil development of Heterodera schachtii and growth of three Beta species. Cycloate added to infested soil enhanced cyst development/gm root on B. vulgaris and larvae/gm of root in B. patellaris and B. procumbens at 4, 16, and 16 μg(a.i.)/gm of soil, respectively. Total numbers of nematodes/individual root system decreased because of poor root growth of seedlings in cycloate-amended soil. Penetration and larval development through stage three did occur in the wild Beta species in any treatment. Thus, resistance of B. patellaris and B. pocumbens to development of H. schachtii was not altered by cycloate. Cycloate also retarded growth (P = 0.05) of the sugarbeet cultivars and B. patellaris at 4 μg(a.i.)/gm and B. procumbens at 16 μg(a.i.)/gm of soil. Higher concentrations of nematodes/gm root in plants growing in cycloate-amended soil may be attributed to factors such as fewer roots available for penetration, possible effects of cycloate on egg hatch, greater attraction of nematodes to roots, and increased susceptibility of roots to larval penetration. Suppression of seedling growth in cycloate-amended soil may be attributed in part to higher nematode density and in part to direct root damage from cycloate.     

Assessment of Parasitic Activity of Fusarium Strains Obtained from a Heterodera schachtii-Suppressive Soil

This study assessed the potential impact of various Fusarium strains on the population development of sugarbeet cyst nematodes. Fungi were isolated from cysts or eggs of Heterodera schachtii Schmidt that were obtained from a field suppressive to that nematode. Twenty-six strains of Fusarium spp. were subjected to a phylogenic analysis of their rRNA-ITS nucleotide sequences. Seven genetically distinct Fusarium strains were evaluated for their ability to influence population development of H. schachtii and crop performance in greenhouse trials. Swiss chard (Beta vulgaris) seedlings were transplanted into fumigated field soil amended with a single fungal strain at 1,000 propagules/g soil. One week later, the soil was infested with 250 H. schachtii J2/100 cm³ soil. Parasitized eggs were present in all seven Fusarium treatments at 1,180 degree-days after fungal infestation. The percentage of parasitism ranged from 17 to 34%. Although the most efficacious F. oxysporum strain 471 produced as many parasitized eggs as occurred in the original suppressive soil, none of the Fusarium strains reduced the population density of H. schachtii compared to the conducive check. This supports prior results that Fusarium spp. were not the primary cause of the population suppression of sugarbeet cyst nematodes at this location.     

Effects of cultural treatments on the incidence of, and damage done by, tomato brown root rot

In soils naturally infested with Pyrenochaeta lycopersici, which usually occurs as a grey sterile fungus (GSF), symptoms of brown root rot (BRR) developed sooner and more extensively in the second year of cropping than in the first. The amount of BRR attributable to corkiness increased as plants aged but, at comparable stages of cropping, decreased in the second and third seasons, an effect associated inversely with the severity of early GSF attack. The larger amount of corkiness, 33 compared with 18 %, on two batches of plants in 1965, each with 53 % end-of-season BRR, was also attributed to a less severe early GSF attack on the former than on the latter, growing in soils unsteamed for 1 and 3 years respectively. The incidence of BRR decreased with increasing depth in infested soils but increased on plants grown in plots with partially sterilized topsoil. Partially sterilizing soils at the G.C.R.I. and Fairfield E.H.S. decreased the incidence of BRR and increased crop weights from about the second month of picking, but fruit quality was poorer. Seasonal yields from plants in untreated soil progressively decreased relatively to those from repeatedly steamed plots, from 93 to 65 % in successive years at Fairfield and from 65 to 56 and 43 % at the G.C.R.I. Steaming done in 1963 and 1964 temporarily retarded GSF attack in 1965 with corresponding yield increases. Increasing the amounts of sterilized propagating soil surrounding roots at planting from 0·4 to 1·01 per plant increased yields by c. 0·4 kg/plant, this being a relatively large increase for plants in infested soil, where this treatment significantly delayed the early incidence of BRR near stem bases. Grafting commercially acceptable scions to rootstocks that tolerated colonization by GSF (‘resistant’ rootstocks), temporarily checked growth, delayed picking and decreased fruit quality. Usually grafted plants, irrespective of soil treatment, yielded at least as much fruit as ungrafted plants in steamed soil. In one of five comparisons, soil steaming increased yields of grafted plants. When testing the effects of previous cropping it seemed that populations of GSF increased similarly in soils planted with grafted and ungrafted plants. In addition to GSF attack, roots at Fairfield E.H.S. were often colonized by Colletotrichum coccodes, microsclerotia (= black dots) being more numerous as plants aged. Although significantly more black dot developed on GSF-resistant rootstocks grown in untreated soil than on those grown in steamed soil, the differences were not associated with effects on yield. C. coccodes colonized GSF-susceptible and -resistant roots equally.     

Development of Heterodera schachtii on Large Rooted Crop Plants and the Significance of Root Debris as Substratum for Increasing Field Infestations

Heterodera schachtii developed to maturity and reproduced on the lateral roots of defoliated sugarbeet which were buried to a depth of 2.5 cm in sterilized soil and inoculated with cysts. Nematodes did not develop on detached lateral roots or on roots of young defoliated beets which did not have a large tap root. The storage roots of large rooted plants were sliced, placed in small jars, inoculated with cysts, covered with moist granulated agar or soil and incubated at 24°C 12-62 days. The sugarbeet nematode developed in root slices of sugarbeet, red table beet, icicle and globe radish, turnip and rutabaga. Only a few males developed on slices of potato tubers. Neither males nor females developed on root slices of carrot, salsify or parsnip. H. schachtii also developed on the cut surfaces of growing sugarbeet and radish.     

Integrated control of potato cyst nematodes using small amounts of nematicide and potatoes with partial resistance

The control of potato cyst nematode (PCN) by less than approved amounts of nematicide combined with partially resistant potato clones was studied in a series of field experiments. On a site heavily infested with Globodera pallida only the most resistant clone (12380ac2) decreased the population density in untreated soil. With aldicarb at its full approved rate (3·36 kg ha^-1) numbers of PCN were decreased under all the genotypes, including the non-resistant Maris Piper. Aldicarb at 1·68 kg ha^-1significantly decreased populations on all clones except 12380ac2. Aldicarb at 0·84 kg ha^-1still significantly decreased population densities and multiplication rates of G. pallida on two clones with intermediate resistance (12243acl and 11233ab22). At two G. rostochiensis sites with light infestations nematode multiplication rates were greater and the control given by aldicarb and partially resistant genotypes of potato was not as great as that at the site with G. pallida. Tuber yields were not increased by the application of aldicarb at the G. rostochiensis infested sites. However, at the site heavily infested with G. pallida the yield of the most intolerant genotype (12380ac2) was increased seven-fold by the full rate of aldicarb (3·36 kg ha^-1) and four-fold by the quarter rate (0·84 kg ha^-1)-Yield of the most tolerant genotype (12243acl) was unaffected by the application of aldicarb.     

Studies on plant growth-regulating substances XLVIII. The effects of3,5-diiodo-4-hydroxybenzoic acid on seedling growth in compact and loose soils

Effects of combinations of insecticides and herbicides on the growth and yield of cauliflower plants (cvs No. 110, Garant and Strong) were determined in two field experiments with seed drilled to give a stand of c. 300000 plants/ha. Granular formulations of chlorfenvinphos or fonofos were applied by the bow-wave method at 2 kg a.i./ha to control cabbage root fly (Delia brassicae). Weeds were successfully controlled with combinations of trifluralin, incorporated into the soil at 0·6 or 1·2 kg a.i./ha before drilling, and propachlor, applied pre-emergence at 2·2 or 4·4 kg a.i./ha. Fonofos, with and without herbicides, significantly lessened (P < 0·01) numbers of seedlings that would survive to harvest. Herbicides and chlorfenvinphos generally did not significantly affect the emergence of healthy seedlings of any cultivar. Combinations of herbicides and chlorfenvinphos were compatible for control of target species. Chlorfenvinphos reduced root damage by at least 50% but did not significantly increase (P > 0·05) the total or marketable weight of curds. Numbers of curds were not usually affected and consistent effects of treatments on maturation periods of the three cultivars were not detected.