Unit 11: Diagnosis of Field Diseases and Pathogens - Practice Quiz

1 What is the first useful step when diagnosing a plant disease in the field?

2 Which term describes a visible response of a plant to disease?

3 Which of the following is a common plant disease symptom?

4 What is a disease sign?

5 Which observation is most helpful for understanding how a disease is distributed in a field?

6 Why should healthy and diseased plants be compared during field diagnosis?

7 Which information should be recorded when collecting a diseased plant sample?

8 Which part of a diseased plant is usually best for laboratory examination?

9 A yellowing of normally green leaves is called what?

10 What does necrosis mean in a diseased plant?

11 Which field instrument is useful for examining small disease signs on leaves?

12 What does a mosaic symptom usually look like on a leaf?

13 Which group of pathogens commonly produces spores and thread-like hyphae?

14 Which causal agent can be seen as tiny worm-like organisms under magnification?

15 Which method is commonly used to observe fungal spores from diseased tissue?

16 Bacterial ooze from infected plant tissue is a sign of which pathogen group?

17 Which laboratory method grows a pathogen on a nutrient medium?

18 Which test detects specific pathogen DNA by making many copies of a target sequence?

19 Which test is commonly used to detect specific pathogen proteins in plant samples?

20 Why are Koch's postulates used in plant pathology?

21 A wheat field shows yellowing plants in irregular patches, while nearby plants remain healthy. Which observation would most strongly support a soil-borne disease rather than a nutrient deficiency?

22 Tomato plants develop wilting during the day but recover overnight. The vascular tissue remains discolored, and soil moisture is adequate. Which diagnostic step is most appropriate next?

23 A farmer reports leaf spots on beans after several days of frequent rain. Which combination of symptoms would best indicate a fungal leaf-spot disease?

24 When surveying a field for disease incidence, which method provides the most reliable estimate?

25 A disease appears mainly in low-lying areas of a field after heavy irrigation. Which field factor should be investigated first?

26 A plant has lesions that are restricted to older leaves, while new leaves remain healthy. Which interpretation is most appropriate during diagnosis?

27 Which field observation best helps distinguish herbicide injury from an infectious plant disease?

28 A plant disease is suspected to be caused by a pathogen carried in irrigation water. Which field pattern would support this hypothesis?

29 During field diagnosis, why should both symptomatic and apparently healthy plants be collected?

30 A cotton field shows plants with stunted growth and malformed leaves in scattered locations. Which additional information would be most useful for diagnosing a possible viral disease?

31 A pathogen produces septate hyphae and chains of dry conidia on infected leaf tissue. Which group is most likely involved?

32 A bacterial disease is suspected in pepper plants. Which laboratory observation would provide the strongest preliminary support?

33 A root sample contains microscopic roundworms with a spear-like stylet. Which pathogen group is indicated?

34 To determine whether a fungus isolated from diseased tissue is the causal pathogen, which procedure is most appropriate?

35 A bacterial isolate from diseased tissue forms cream-colored colonies and causes a hypersensitive response on a nonhost leaf. What does the response primarily indicate?

36 A root disease is associated with spherical galls containing swollen females. Which causal organism is most likely?

37 A diseased plant shows mosaic patterns and severe leaf curling, but no fungal structures are visible. Which test would best help identify a virus as the causal pathogen?

38 A fungus is isolated from a lesion, but it is also found on dead plant debris. Which evidence is most important before identifying it as the primary pathogen?

39 Which feature is most useful for distinguishing a fungal pathogen from a bacterial pathogen during microscopic examination?

40 A pathogen is detected by PCR in both diseased and healthy plants. Which conclusion is most scientifically appropriate?

41 A tomato field shows interveinal chlorosis and stunting concentrated near the entrance where equipment turns. Roots lack lesions or vascular discoloration, and symptomatic plants test negative for common viruses. Soil analysis reveals a sharp pH increase in the affected zone. Which diagnosis is best supported?

42 A fungus is repeatedly isolated from the advancing margins of leaf lesions, but inoculation of healthy plants produces symptoms only after the leaves are mechanically wounded. Unwounded controls and unwounded inoculated plants remain healthy. What is the most defensible interpretation?

43 After application of a microbial biofungicide, lower leaves develop irregular necrotic spots within 18 hours. The lesions occur uniformly across treated rows, do not expand after 48 hours, and cannot be transmitted to healthy plants. Which conclusion is most appropriate?

44 A real-time PCR assay targeting a suspected pathogen gives for diseased tissue, for asymptomatic tissue, no amplification in the extraction blank, and for the positive control. Which additional result would most strongly support causal involvement rather than incidental detection?

45 Wilted plants occur in elongated patches aligned with the direction of irrigation. Cutting the lower stem reveals unilateral vascular browning, and wilt persists overnight despite adequate soil moisture. Which inference best integrates these observations?

46 Sequencing the ITS region from a diseased root produces a 100% database match to three closely related Fusarium species that differ in host range and toxin production. What is the best next step for species-level identification?

47 In a field trial, disease incidence is 70% in untreated plots and 25% in plots receiving a bacterial biocontrol agent. However, treated plots were planted with a different cultivar and occupy the better-drained half of the field. Which statement is justified?

48 A bacterium isolated from a leaf spot is Gram-negative, oxidase-negative, and fluorescent on King's B medium. A genus-specific PCR is positive, but a pathovar-specific PCR is negative. Which conclusion is most scientifically defensible?

49 A disease survey samples ten adjacent plants at one location in each of 30 fields. The objective is to estimate field-level disease incidence, but symptoms occur in compact clusters. What is the principal flaw in this design?

50 Virus-like mosaic symptoms occur in a crop, but ELISA is negative. The internal positive control reacts normally, while sap from symptomatic plants was stored for a week at room temperature before testing. Which follow-up is most appropriate?

51 A foliar disease appears first on the windward border of a field and declines with distance inward. After a week of storms, new foci also appear around scattered volunteer host plants. Which epidemiological interpretation best fits both patterns?

52 Metabarcoding of necrotic roots detects abundant reads from an oomycete and lower numbers from several fungi. Mock-community controls reveal that the oomycete primers amplify its DNA about ten times more efficiently than fungal DNA. What can be concluded from read abundance alone?

53 A root disease occurs only in waterlogged sections of a field. Improving drainage prevents symptoms, yet the suspected oomycete can still be detected at low levels in asymptomatic, well-drained soil. Which disease model best explains the findings?

54 A suspected obligate biotrophic fungus cannot be grown on artificial medium. Which approach most appropriately adapts causal testing to this biological constraint?

55 Two disorders produce similar marginal leaf scorch. Disorder X begins on older leaves and is uniform across plants on sandy ridges; disorder Y begins on scattered leaves and later develops bacterial ooze. Which observation has the greatest differential diagnostic value?

56 A qPCR assay detects a pathogen in 18 of 20 symptomatic plants and 7 of 20 asymptomatic plants. The pathogen concentration is consistently much higher in symptomatic plants, but viable organisms have not been recovered. Which statement best describes the evidence?

57 Disease severity is recorded on a 0-5 ordinal scale before and after treatment. A researcher subtracts the mean post-treatment score from the mean pretreatment score and concludes that the pathogen population declined. What is the central diagnostic limitation?

58 A fungal isolate reproduces field symptoms on cultivar A but not cultivar B. The original outbreak occurred only on cultivar A, although both cultivars were exposed in the same field. How should the negative result on cultivar B be interpreted?

59 Following application of a Trichoderma-based product, laboratory plates from treated roots are rapidly overgrown by Trichoderma, while a suspected pathogen is rarely recovered. Field symptoms remain unchanged. Which conclusion is most appropriate?

60 A multiplex diagnostic assay contains a pathogen target and a plant internal amplification control. A symptomatic sample is negative for both targets, whereas all external controls perform correctly. What is the best interpretation?