New maize inbreds in Argentina. II. Reponse to Puccinia sorghi (Schw.) --Corcuera, VR, Sandoval, MC During the growing season 2000/01 a field trial was conducted at the Inst. Fitotécnico de Sta. Catalina in order to measure the ability and competitiveness of different inbreds developed during the last years within a qualitybreeding programme held at our Institution. Amongst several agronomic traits, respone to "maize common rust" was determined considering: 1) attack severity or % of leaf area with pustules (based on the visual scale developed by Peterson et al., 1948 for Wheat orange rust) and 2) type or degree of infection, based on a modification of Cobb´s scale as follows:
 
No. pustules/leaf Severity % Degree of infection Behaviour to pathogen
<11 <5 I Very resistant
12-19 6-10 II Resistant
20-38 11-25 III Mid-resistant
39-67 26-40 IV Mid-susceptible
68-83 41-65 V Susceptible
>84 66-100 VI Very susceptible

Measurements in the field were taken one month after anthesis and 3 leaves/plant were considered (those of the upper ear and one leaf up and down). Twenty-four plants per inbred (3 repetitions) were observed and their data were averaged. Table 1 summarizes all data collected and gives the respone of each inbred to the pathogen. Attack severity data were transformed into arcsin according to Snedecor G(1962) and then an ANOVA test was performed within inbreds with the same type of endosperm (normal or modified). In all the cases analyzed, the differences found amongst averages were due only to variation of the genotype, so no environmental influence exists. In spite of this, the different inbreds can be grouped depending on their average values for attack severity (see Tables 2 and 3). There are 5 different groups in modified endosperm maize and only 3 in normal endosperm inbreds.

Of all the inbreds studied during 2000/01 under natural infection conditions, 5 inbreds were very resistant to maize common rust, 10 were resistant, 11 were mid-resistant, 10 were susceptible and 2 were very susceptible. Inbreds 3131, 3135, 3136b and 3139 which are very resistant to "maize common rust" attack, are quality protein maizes and they carry in their background the opaque-2 gene from the same progenitor (inbred 7515 Mazoti). Likewise, the inbreds 3022c, 3135 and 3136b which are also very resistant derive from the same progenitor (FW) and normal inbreds 3027 and 3028 came from the progenitor CP27. Finally we want to stress the fact that 10 new inbreds resistant to Puccinia sorghi (Schw.) and obtained within a quality breeding programme, are available to develop new hybrids in Argentina.

Table 1. List of Materials evaluated and their behaviour to Puccinia sorghi(Schw.).
 
  Pedigree Generation Endosperm Severity(%) No. Pustules Infection Grade Behaviour*
  2000-3098 OPACO2 LE 11a 25 24 III MR
  2000-3092 OPACO2 LE 11 a 25 24 III MR
  2000-3088 OPACO2 S7 6A10 17 II-III R
  2000-3130 OPACO2 S1 41A65 81 IV MS
  2000-3141 NOR/OPAC2 S1 66-100 114 VI S
  2000-3142 NOR/OPAC2 S1 66-100 98 VI S
  2000-3131 NOR/OPAC2 S1 5 10 II R
  2000-3132 NOR/OPAC2 S1 11 A 25 36 III-IV MR
  2000-3133 NOR/OPAC2 S1 6 A 10 17 II R
  2000-3134 o2/cshwx S1 11 A 25 29 II-III R
  2000-3135 o2/cshwx S4 <5 8 II R
  2000-3096b o2/cshwx S3 26 A 40 43 IV MS
  2000-3096c o2/cshwx S4 11 A 25 20 III-IV MR
  2000-3096a o2/cshwx S3 11 A 25 30 III-IV MR
  3136b o2/cshwx S3 0 0 I VR
  2000-3137 nor/cshwxo2 S1 11 A 25 28 III MR
  2000-3138 nor/o2/o5 S1 41 A 65 60 III-V MS
  2000-3139 o2/o2Oh43 S1 <5 9 II R
  2000-3022c nor/wx S7 0 0 0 VR
  2000-3022b nor/wx S7 <5 6 II R
  2000-3072 nor/wx S3 26 a 40 60 IV MS
  2000-3002a wx S4 65 72 IV MS
  2000-3002c wx S6 26 a 40 57 IV MS
  2000-3043a normal LE 11 a 25 37 III-IV MR
  2000-3043b normal LE 26 a 40 62 IV MS
  2000-3063a normal S2 11 a 25 36 III MR
  2000-3063b normal S3 41 a 65 75 IV-V MS
  2000-3140 normal S2 40 67 IV MS
  2000-3165 normal S2 <11 5 I-II R
  2000-3031 normal S6 26 a 40 46 IV MS
  2000-3008a  normal S5 <11 5 I-II R
  2000-3043a normal LE 11 a 25 37 III-IV MR
  2000-3027 normal S5 <5 8 0-I VR
  2000-3071 normal S4 10 19 II R
  2000-3011 normal S3 <5 3 0-I VR
  2000-3028 normal S3 <5 2 0-I VR
  2000-3057 normal S4 25 35 III MR
  2000-3136a o2/cshwx S2 26 a 40 44 III-IV MR

*: VR: very resistant, MR: mid-resistant, MS: mid-susceptible, S: susceptible

Table 2. Comparison of means of "attack severity" to Puccinia sorghi (Schw.) in modified endosperm maize.
 
Genotype Endosperm Average Groups(1)
3142 NOR/OPAC2 77.30 A
3141 NOR/OPAC2 75.00 A
3130 OPAQUE2 46.53 B
3096b o2/cshwx 35.40 BC
3098 OPAQUE2 28.63 BCD
3092 OPAQUE2 28.17 BCD
3096c o2/cshwx 27.50 BCD
3132 NOR/OPAC2 25.13 CD
3096a o2/cshwx 24.47 CD
3137 nor/cshwxo2 24.43 CD
3134 o2/cshwx 24.20 CD
3088 OPAQUE2 16.70 CDE
3133 NOR/OPAC2 16.33 CDE
3135 o2/cshwx 11.83 DE
3131 NOR/OPAC2 11.05 DE
3022c NOR/wx 0.00 E
3022b NOR/wx 0.00 E
3136b o2/cshwx 0.00 E

(1) Averages followed by the same letters do not differ significantly at 1% of probability

Table 3. Comparison of means of "attack severity" to Puccinia sorghi (Schw.) in normal endosperm maize.
 
Genotype Media  
3063b 53.73 A
3043b 34.37 B
3031 33.95 B
3057 29.78 B
3043a 24.82 BC
3071 18.45 BC
3028 13.23 C
3027 12.91 C
3008a 11.97 C

*: averages followed by the same letter do not differ significantly at 1% probability.
 
 

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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