Figure 1.
Maize and pepper intercropping in field and the effect on the development of pepper Phytophthora blight.
(A) Maize and pepper intercropping and monoculture patterns. Each symbol represents a plant of a different crop species: maize (×), pepper (○). In maize monoculture system, the wide inter-row spacing was 100 cm and the narrow inter-row spacing was 50 cm. The intra-row spacing was 25 cm; In pepper monoculture system, the inter-row and intra-row spacing were 30 cm×30 cm in each strip. The space between strips was 120 cm. In maize and pepper intercropping system, the width of each strip was 3.4 m, and one row of maize intercropping with nine rows of pepper was planted in each strip. The inter-row and intra-row spacing for pepper plant was 30 cm×30 cm. The intra-row spacing of maize plant was 25 cm. The inter-row spacing between maize and pepper plants was 60 cm; (B) Maize and pepper intercropped in field; (C) Pepper Phytophthora blight in intercropping system. Arrow shows the disease center. Maize can restrict pepper Phytophthora blight across the maize line; (D) Disease severity (±SE) of pepper Phytophthora blight in monoculture and maize/pepper intercropping system from 2009 to 2011. Asterisks indicate statistically significant differences of monoculture compared to intercropping (Student's t test; p<0.05; n = 10); (E) Effect of maize with different intra-row spacing on the disease severity of pepper Phytophthora blight incidence (±SE) in intercropping system in 2012. Asterisks indicate statistically significant difference of severity surveyed in August and June (Student's t test; p<0.05; n = 5). M and I in figure D and E represent pepper monoculture and pepper intercropping with maize, respectively.
Figure 2.
Effect of maize plant with different intra-row spacing on the root architecture and the spread of pepper Phytophthora blight in the greenhouse.
(A) A schematic illustration of maize and pepper intercropping arrangements in the greenhouse. Maize planted with six different intra-row spacing distances (10, 15, 20, 25, 35 and 45 cm). Each plot contains two lines of maize with different intra-row spacing. Two lines of pepper were planted between the two lines of maize, and one line of pepper was sown outside of each maize line as an indicator line. Six peppers in the center of two pepper lines were inoculated with zoospores of P. capsici. The incidence of pepper Phytophthora blight in indicator lines was surveyed to show the ability of the zoospores to spread; (B) Changes in maize root architecture with different intra-row spacing distances at silking stage; (C) Effect of maize intra-row spacing on the spread of pepper Phytophthora blight in plastic houses. M and I represent pepper monoculture and pepper intercropping with maize, respectively. Means and standard errors are shown. Different letters indicate statistically significant differences analyzed using Turkey Post-Hoc ANOVA (p<0.05; n = 9); (D) The correlation analysis between disease incidence and maize root biomass in each line at silking stage.
Figure 3.
The accumulation and secretion of DIMBOA and MBOA in root under different maize plant distances.
(A) A schematic illustration of maize grown at three distances 5 cm×5 cm, 10 cm×10 cm, and 20 cm×20 cm; (B) Accumulation of DIMBOA and MBOA in roots and shoots of maize grown at the three distances. Data represents mean values in µg g−1 fresh weight (FW) from three replicated samples; (C) The content of DIMBOA and MBOA in maize rhizosphere soil. Different letters designate significant differences analyzed using Turkey Post-Hoc ANOVA (p<0.05; n = 3).
Figure 4.
Interaction of pepper and maize roots with Phytophthora capsici zoospores.
A∼C shows the interaction of pepper root and zoospores. Zoospores were attracted to the root elongation zone of pepper, quickly stopped and encysted into cystospores on the root surface or near the root. And then cystospores began to germinate. Arrow in C shows the germinated spores. D∼F shows the interaction of maize root and zoospores. Zoospores were attracted to the root tip of maize, quickly stopped and encysted into cystospores. Few cystospores germinated and some cystospores on the root tip of maize ruptured. Arrow in F shows the ruptured cystospores. G∼I shows the interaction of zoospores and the root of maize BX1 mutant, which can not produce DIMBOA and MBOA. Zoospores were also attracted to the root tip zone, quickly stopped and encysted into cystospores. However, most of cystospores did not rupture but germinated after 30 min incubation. Arrow in I shows the germinated cystospores.
Figure 5.
The inhibitory activity of maize root exudates on different life stages of Phytophthora capsici.
A and B show the inhibitory activity of root exudates collected from the variety Haihe-1 and Genyuan-135 against the zoospore release, motility, cystospore germination, and colony growth of P. capsici. C and D show the effect of root exudates of Haihe-1 and Genyuan-135 on cystspore rupture, respectively. Error bars indicate SE (n = 3) of three replicates.
Figure 6.
The inhibitory activity of compounds BZO (A), MBZO (B) and MBOA (C) against the release of zoospores from sporangia, zoospore motility, cystospore germination and colony growth of Phytophthora capsici.
Error bars indicate SE (n = 3) of three replicates.