Red rust

PATHOLOGY

1. COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po), ViaVaigai Dam, Theni-625 562 Algal Spot or Red Rust in Horticultural Crops (Mango , Guava, Tea) SUBMITTED BY COURSE TEACHER ALWIN F Dr. PARTHASARATHY. S 2015021008 Asst . Prof (Plant Pathology)

2. RED RUST IN HORTICULTURAL CROPS Red rust / Algal leaf spot Asexual stage : Cephaleuros virescens Cephaleuros mycoides Cephaleuros parasiticus

3. Classification Kingdom: Archaeplastida Phylum: Chlorophyta Class: Ulvophyceae Order: Trentepohliales Family: Trentepohliaceae Genus: Cephaleuros Species: C. virescens

4. Significance Algal leaf spot is a minor disease of little economic importance, although it can result in leaf fall, dieback of branches, or distortion of fruits.

5. Distribution The pathogen is world wide in distribution – In tropics and sub tropics Host Plants Tea, Kava, Pepper , Magnolia, Coffee , Oil Palm, Avocado , Vanilla, Mango , Breadfruit, Guava, Coconut , Cacao, Citrus.

6. Symptoms On leaves, green to orange spots develop, which are round, 2-4 mm diameter, flattened with furry growth and indistinct margins. The spots may merge. © www.growables.org

7. On young stems, the spots cause cracks in the bark and this can lead to dieback. Spores of the algae (called sporangia) are formed on the spots, giving them a furry look. ©www.pestnet.org ©www.pestnet.org

8. © www.plantvillage.psu.edu © www.plantvillage.psu.edu Red rust in Guava

9. ©www.flickr.com ©www.agritech.tnau.ac.in Red rust in Mango Red rust in Tea

10. Spread Primary and secondary spread is through air borne zoospores. Survival The pathogens reproduce and survive in spots on leaves or stems and in fallen plant host debris. Favourable condition Poor nutrition, poor soil drainage and too much or too little shade

11. Identification of pathogen Aerophilic , filamentous green algae. Although, they require a film of water to complete their life cycles. Produces a disc like thallus which comprises of symmetrically arranged barrel shaped cells which grow dichotomously from the centre to the peripherry of the thallus . The centre of the thallus is multilayered while the peripherry is single layered.

12. The cells have cholorophyll a, b and carotenoid as photosynthetic pigments and cell wall contains cellulose, xylan , mannan etc. Usually it grows between the cuticle and epidermis of the host tissue and very rarely between epidermis and palisade cells. Conidiophores and Macro Conidia of Bakane Disease ©www.scielo.br

13. The host cells below this assume a corky appearance and prevent further penetration of algae. Rhizoids arise from the thallus extend to the underlying cells ( cuticle and epidermis ) by the mechanical forces of thallus and not by any enzymatic dissolution of host surface. The rhizoids act as anchoring as well as absorbing organ and get nourishment by osmosis

14. ©www.researchgate.net

15. ©Plant pathology , Dr. B.P.Pandey , Pg - 281

16. Disease Cycle Hosts are inoculated when sporangia or thallus fragments with sporangia are deposited on susceptible host tissues. Infection occurs and symptoms develop under moist conditions when motile zoospoores are released from the sporangia, penetrate the host cuticle, and generate disc-like algal thalli with thread like algal filaments.

17. Management Sanitation : Remove spotted leaves by hand from lightly diseased plants; prune low hanging branches that are affected by the disease; collect and discard all fallen leaves. Pruning : Prune overhanging trees around diseased plants (this will reduce relative humidity and speed up leaf drying after rains). Reduce plant stress : Keep plants well fertilized; improve soil drainage.

18. Weed control : Keep weeds around affected plants under control (this will reduce relative humidity in the plant canopy and reduce plant stress); prevent climbing and vine-like weeds from establishing on the host plant. Intercropping : Interplant very susceptible hosts with less susceptible hosts. Variety selection : try to select a more tolerant variety (for example, of guava) where the crop is grown in a wet environment.

19. Choice of planting location : for highly susceptible crops, select a planting location with moderate rainfall, well drained soil and good air circulation. Manage : plant spacing and thinning to improve aeration and light exposure. Fungicides : Some fungicides will provide control; use chemicals only according to directions on the label; the Bordeaux mixture is commonly recommended. Spray COC @ 0.25 % .